Sen. Max Baucus (D-Mont.) won't seek reelection in 2014, the Washington Post reported on Tuesday.

Baucus would have been running for his seventh term in 2014. He currently serves as Senate Finance Committee chairman. Sen. Ron Wyden (D-Ore.) is now next in line for the gavel, with Sen. Jay Rockefeller (D-W.Va.), the Democrat next in seniority, also set to retire.

The 72-year-old Montana Democrat recently cast a critical vote against a bipartisan Senate amendment that would have expanded background checks for gun purchases. Baucus also backed the Bush tax cuts of 2001 and emerged as a key supporter of President Barack Obama's 2010 health care reform law.

Baucus's vote against background checks drew a quick response from the Progressive Change Campaign Committee, which targeted Baucus and other opposing Democrats in an ad campaign accusing them of refusing to "support sensible gun laws, and keep our families and communities safe."

PCCC co-founder Stephanie Taylor offered Baucus a stinging farewell on Tuesday.

"Good bye, Senator K Street. Max Baucus has a history of voting with corporate interests and not the interests of Montana voters -- taking millions from Wall Street, insurance companies, and lobbyists," she said in a statement. "Montana will finally have a chance to have a senator with its best interests at heart, and we hope [former Democratic Gov.] Brian Schweitzer jumps into the race immediately."

As the Associated Press reports:

Baucus' retirement opens up an opportunity for Republicans to claim a Senate seat in a state where GOP presidential nominee Mitt Romney easily defeated Obama by 12 percentage points last year. But Democrats have proved resilient in Montana, with Sen. Jon Tester winning re-election last year. The election of Steve Bullock last year is the third term in a row in which Democrats have held the governorship.

Schweitzer is thought to be a potential contender for the open Senate seat. The Democrat spoke about a potential run for national office last week, saying that his views on issues such as gun control could hurt his chances if he were to seek the presidency.

Speaking at Montana State University, Schweitzer boiled down his position on guns to, "You control yours, I’ll control mine.”

With Baucus' announcement, eight senators have now announced plans to retire ahead of the next election cycle. Six are Democrats and two are Republicans.

More from the Associated Press:

Democrats in the Senate will be defending 21 seats next year to Republicans 14, with several Democrats running for re-election in GOP-leaning states that Romney won handily. Among the Democrats facing tough challenges next year are Sens. Mark Begich of Alaska, Mary Landrieu of Louisiana and Mark Pryor of Arkansas.

Democrats also have more retirements than the GOP. Five more Democrats have announced they will not seek another term: Jay Rockefeller of West Virginia, Tom Harkin of Iowa, Frank Lautenberg of New Jersey, Carl Levin of Michigan and Tim Johnson of South Dakota.

Among Republicans, Saxby Chambliss of Georgia and Mike Johanns of Nebraska have decided to retire.

UPDATE: 12:20 p.m. -- Baucus released a statement addressing his decision to retire:

“Serving the people of Montana has been the greatest honor and privilege of my life. Over the past 35 years, I have been lucky to go from working for just under 800,000 of the world’s best bosses to more than a million – and I am grateful to each and every one of them for the opportunity they have given me.

“When I first asked my hero and mentor Mike Mansfield whether I should run for U.S. Senate nearly 40 years ago, he told me it would take a lot of hard work, a lot of shoe leather, and a bit of luck. In the next year and a half, I want to spend all my hard work, shoe leather and luck working for the people of Montana instead of on campaigning.

“So, after much consideration and many conversations with my wife Mel and our family, I have decided not to seek reelection in 2014. I will serve out my term, and then it will be time to go home to Montana.

“But, I’m not turning out to pasture because there is important work left to do, and I intend to spend the year and a half getting it done. Our country and our state face enormous challenges – rising debt, a dysfunctional tax code, threats to our outdoor heritage, and the need for more good-paying jobs.

“I’m ready to roll up my sleeves and get to work. I will double down on legislation to permanently protect the American side of the North Fork watershed and keep the Rocky Mountain Front the way it is for future generations. I am going to put everything I’ve got into leaving Montana with strong Highway and Farm Bills that support jobs in our state. And I’m going full steam ahead to put on the best Economic Development Summit yet.

“At a national level, I will continue to work on simplifying and improving the tax code, tackling the nation’s debt, pushing important job-creating trade agreements through the Senate, and implementing and expanding affordable health care for more Americans.

“Deciding not to run for re-election was an extremely difficult decision. After thinking long and hard, I decided I want to focus the next year and a half on serving Montana unconstrained by the demands of a campaign. Then, I want to come home and spend time with Mel, my son Zeno, and our family enjoying the Montana public lands we’ve fought hard to keep open and untarnished.

“Above all else, I want Montanans to know how grateful and humbled I am to have had the privilege of serving them, and I look forward to working with them as I continue to serve the state I love for the next year and a half.”

UPDATE: 2:40 p.m. -- Obama released a statement concerning Baucus' retirement:

I want to thank Max Baucus for his nearly 35 years of service to the people of Montana. Max has made small businesses a top priority, often taking “Work Days” to visit local businesses across Montana and spend a day working alongside his constituents to gain perspective and help bolster the local economy. As Finance Committee Chairman and a senior member of both the Agriculture and the Environment and Public Works Committees, Max has been a leader on a broad range of issues that touch the lives of Americans across the country. Michelle and I commend Senator Baucus on his career, and wish him and his family well in the future.
This story is developing. Check back for updates...

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  • Max Baucus To Retire

    In April 2013, Sen. Max Baucus (D-Mont.) announced that he would <a href="http://www.huffingtonpost.com/2013/04/23/max-baucus-retiring_n_3138758.html" target="_blank">not seek reelection</a> in 2014. The Senate Finance Committee chairman has stood out from the Democratic pack, making moves many progressives have seen as cringeworthy. Here's a look back at some of his most noteworthy moments. (AP Photo/J. Scott Applewhite)

  • Taxes

    Baucus has been at odds with fellow Democrats on the issue of <a href="http://www.nytimes.com/2013/04/07/us/politics/tax-lobby-builds-ties-to-max-baucus.html?pagewanted=all&_r=0" target="_blank">taxes</a> for quite some time. Unlike most in his party, he aligned himself with President George W. Bush's 2001 tax cuts for the wealthy. In March 2013, he voted against the Democrats' 2014 budget proposal. (Photo by Scott J. Ferrell/Congressional Quarterly/Getty Images)

  • Melodee Hanes Nomination

    In 2009, <a href="http://www.huffingtonpost.com/2009/12/08/baucus-girlfriend-melodee_n_383781.html" target="_blank">Baucus nominated his then-girlfriend</a> Melodee Hanes -- who also had served as his state director -- for the position of U.S. attorney. Hanes later withdrew her nomination because of her connection to Baucus. The couple <a href="http://www.huffingtonpost.com/2011/07/03/max-baucus-marries-melodee-hanes-married_n_889373.html" target="_blank">married</a> in 2011. (AP Photo/Pablo Martinez Monsivais, File)

  • DREAM Act Vote

    Baucus was one of only five Democratic senators to vote against the <a href="http://www.huffingtonpost.com/2010/12/18/dream-act-vote-senate_n_798631.html" target="_blank">DREAM Act</a> in 2011, causing the bill to fail. (AP Photo/J. Scott Applewhite)

  • Health Care Reform Delay

    Baucus was the key Democratic senator to <a href="http://www.huffingtonpost.com/2009/09/16/baucus-conrads-miserable_n_289253.html" target="_blank">delay health care reform</a> in 2009. He held up health care debates to try to make deals with GOP senators in an attempt at bipartisanship. He <a href="http://www.huffingtonpost.com/2009/09/16/health-care-bill-baucus-s_n_288218.html" target="_blank">unveiled a bill</a> that called for compromise, but instead of bringing the parties together, it irked both sides. (Photo By Bill Clark/Roll Call/Getty Images)

  • PhRMA Bill

    Baucus proposed a <a href="http://www.huffingtonpost.com/2009/09/18/baucus-bill-sticks-to-pha_n_290639.html" target="_blank">health care reform bill</a> in 2009 that was attacked as a giveaway to the Pharmaceutical Research and Manufacturers of America (PhRMA) and insurance companies. The senator's connection to the health care lobbyist complex came under fire. (AP Photo/J. Scott Applewhite)

  • Obamacare 'Train Wreck'

    Never one to avoid crossing party lines, Baucus said in April 2013 that he thought Obamacare is headed for "<a href="http://www.huffingtonpost.com/2013/04/17/max-baucus-obamacare_n_3101801.html?utm_hp_ref=politics" target="_blank">a huge train wreck</a>." He is the first top Democrat to voice public concerns about the implementation of the health care law. (AP Photo/J. Scott Applewhite)

  • Background Check Vote

    Baucus was <a href="http://www.huffingtonpost.com/2013/04/17/background-checks-bill_n_3103341.html" target="_blank">one of four Democratic senators to oppose</a> expanding background checks when that gun reform legislation came to the Senate floor and failed in April 2013, just a week before he announced his retirement. (AP Photo/J. Scott Applewhite)

  • 'YouTubes'

    Baucus drew laughs in 2009 when he was swarmed by protesters carrying what he called "<a href="http://www.huffingtonpost.com/2009/08/19/max-baucus-is-scared-of-t_n_263284.html" target="_blank">YouTubes</a>" -- he meant cameras. (AP Photo/J. Scott Applewhite)