LINCOLN, Neb. -- The Republican primary to replace U.S. Sen. Mike Johanns in Nebraska could unfold as an open-and-shut contest or a wide-open race, depending on what Gov. Dave Heineman decides.

Heineman would enter the 2014 election as a heavy favorite if he chooses to run for the seat, and his decision to run likely would keep other GOP hopefuls from joining the contest, party officials and strategists said Tuesday. Conversely, a decision by Heineman not to run would unleash a flurry of candidates without an obvious front-runner.

Johanns announced Monday that he would not seek re-election in 2014, saying he and his wife wanted to move to a new phase of their lives after a 32-year career in public service. Heineman said Monday he is considering a run for the seat, but he stressed during an unplanned news conference that he had not decided one way or the other.

Heineman, the state's longest-serving governor, has enjoyed fairly consistent approval ratings in the 60s and 70s, according to several polls. He also has statewide name recognition, a pulpit to garner press attention and a robust fundraising network from his two prior campaigns. He was twice elected governor with more than 70 percent support.

"With all of those advantages, I just can't possibly see anyone else getting in if the governor decides that he wants to run," said Jordan McGrain, executive director of the Nebraska Republican Party. "If he doesn't, look out. The flood gates will open."

Nebraska remains solidly Republican, with the GOP holding all statewide offices as well as its three congressional districts. Republicans expanded their control last year's U.S. Senate race, when then-state Sen. Deb Fischer defeated Democrat Bob Kerrey.

Heineman was courted by national party officials after Democratic U.S. Sen. Ben Nelson announced in December 2011 that he was retiring. But he declined to enter the race at the time, saying he wanted to focus on his work as governor. Heineman is leaving office in 2015 because of term limits.

"He's a tier one candidate and everyone knows it," said Nebraska Republican consultant Sam Fischer, a partner at Meridian Strategies in Omaha. "I think it makes people think a lot harder about challenging Gov. Heineman. He's still immensely popular in the state, and I think it's potentially a primary-clearing event."

Fischer said Heineman also has the luxury of waiting for as long as several months, whereas other candidates will have to start campaigning by the start of summer to have a shot.

"To me, if they're serious, they're going to have to get their ducks in a row and hit the road by early summer," Fischer said. "With the summer, you've got all the fairs and parades. For people who are lesser-known in the state, in my opinion, they're going to have to look at getting in by June 1."

Johanns' decision to not to seek re-election has drawn attention to a field of possible candidates from both parties, although none have announced or indicated how they're leaning. The Republican possibilities include U.S. Reps. Jeff Fortenberry, Adrian Smith and Lee Terry, Nebraska Attorney General Jon Bruning, state Treasurer Don Stenberg and former state Treasurer Shane Osborn.

Fortenberry has said he is considering a run for the seat. The five-term congressman ended 2012 with nearly $771,000 in cash on-hand that could be used in a U.S. Senate campaign, according to federal election records. Terry finished the year with $21,000, and Smith had $628,000.

The possible Democratic U.S. Senate candidates include former University of Nebraska Regent Chuck Hassebrook, Lincoln Mayor Chris Beutler, former Lt. Gov. Kim Robak, and former gubernatorial candidate Mike Meister, a Scottsbluff attorney.

Vince Powers, chairman of the Nebraska Democratic Party, said if Heineman chooses to run for Senate he could face criticism for his administration's handling of problems at the Beatrice State Developmental Center and within Nebraska's child welfare system.

"The Republicans have been in power for so long that it leads to arrogance and scandal and corruption," he said.

Also on HuffPost:

Loading Slideshow...
  • Sen. Jeff Flake (R-Ariz.)

    U.S. Sen. Jeff Flake (R-AZ) (L) participates in a reenacted swearing-in with his wife Cheryl Flake (C) and U.S. Vice President Joe Biden in the Old Senate Chamber at the U.S. Capitol January 3, 2013 in Washington, DC. (Photo by Chip Somodevilla/Getty Images)

  • Sen. Chris Murphy (D-Conn.)

    Vice President Joe Biden administers the Senate Oath to Sen. Chris Murphy, D-Conn., accompanied by his wife Catherine and sons Rider and Owen, right, during a mock swearing in ceremony on Capitol Hill in Washington, Thursday, Jan. 3, 2013, as the 113th Congress officially began. (AP Photo/ Evan Vucci)

  • Sen. Mazie Hirono (D-Hawaii)

    U.S. Sen. Mazie Hirono (D-HI) (L) participates in a reenacted swearing-in with U.S. Vice President Joe Biden in the Old Senate Chamber at the U.S. Capitol January 3, 2013 in Washington, DC. (Photo by Chip Somodevilla/Getty Images)

  • Sen. Joe Donnelly (D-Ind.)

    U.S. Sen. Joe Donnelly (D-IN) (L) participates in a reenacted swearing-in with his wife Jill Donnelly and U.S. Vice President Joe Biden in the Old Senate Chamber at the U.S. Capitol January 3, 2013 in Washington, DC. (Photo by Chip Somodevilla/Getty Images)

  • Sen. Elizabeth Warren (D-Mass.)

    U.S. Sen. Elizabeth Warren (D-MA) (L) participates in a reenacted swearing-in with her husband Bruce Mann and U.S. Vice President Joe Biden in the Old Senate Chamber at the U.S. Capitol January 3, 2013 in Washington, DC. (Photo by Chip Somodevilla/Getty Images)

  • Sen. Angus King (I-Maine)

    U.S. Sen. Angus King (I-ME) (L) participates in a reenacted swearing-in with his wife Mary Herman and U.S. Vice President Joe Biden in the Old Senate Chamber at the U.S. Capitol January 3, 2013 in Washington, DC. (Photo by Chip Somodevilla/Getty Images)

  • Sen. Heidi Heitkamp (D-N.D.)

    U.S. Sen. Heidi Heitkamp (D-ND) (L) participates in a reenacted swearing-in with her husband Darwin Lange (C) and U.S. Vice President Joe Biden in the Old Senate Chamber at the U.S. Capitol January 3, 2013 in Washington, DC. (Photo by Chip Somodevilla/Getty Images)

  • Sen. Deb Fischer (R-Neb.)

    Vice President Joe Biden administers the Senate Oath to Sen. Deb Fischer, R-Neb., accompanied by her husband Bruce Fischer, during a mock swearing in ceremony on Capitol Hill in Washington, Thursday, Jan. 3, 2013, as the 113th Congress officially began. (AP Photo/Cliff Owen)

  • Sen. Martin Heinrich (D-N.M.)

    U.S. Sen. Martin Heinrich (D-N.M.) (2nd L) participates in a reenacted swearing-in with his wife Julie Heinrich, sons Carter and Micah, and U.S. Vice President Joe Biden in the Old Senate Chamber at the U.S. Capitol January 3, 2013 in Washington, DC. (Photo by Chip Somodevilla/Getty Images) <em><strong>CORRECTION:</strong> A previous version of this image mislabeled Sen. Heinrich's party affiliation. He is a Democrat.</em>

  • Sen. Tim Scott (R-S.C.)

    U.S. Sen. Tim Scott (R-SC) (L) participates in a mock swearing-in with his mother Frances Scott and U.S. Vice President Joe Biden in the Old Senate Chamber at the U.S. Capitol January 3, 2013 in Washington, DC. (Photo by Chip Somodevilla/Getty Images)

  • Sen. Ted Cruz (R-Texas)

    U.S. Sen. Ted Cruz (R-TX) (L) participates in a reenacted swearing-in with his wife Heidi Nelson Cruz, daughters Caroline and Catherine, and U.S. Vice President Joe Biden (R) in the Old Senate Chamber at the U.S. Capitol January 3, 2013 in Washington, DC. (Photo by Chip Somodevilla/Getty Images)

  • Sen. Tim Kaine (D-Va.)

    U.S. Sen. Tim Kaine (D-VA) (L) participates in a reenacted swearing-in with his wife Anne Bright Holton and U.S. Vice President Joe Biden in the Old Senate Chamber at the U.S. Capitol January 3, 2013 in Washington, DC. (Photo by Chip Somodevilla/Getty Images)

  • Sen. Tammy Baldwin (D-Wis.)

    WASHINGTON, DC - JANUARY 03: U.S. Sen. Tammy Baldwin (D-WI) (L) participates in a reenacted swearing-in with U.S. Vice President Joe Biden in the Old Senate Chamber at the U.S. Capitol January 3, 2013 in Washington, DC. (Photo by Chip Somodevilla/Getty Images)

  • Sen. Brian Schatz (D-Hawaii)

    Vice President Joe Biden, right, re-enacts the swearing in of Sen. Brian Emanuel Schatz, D-Hawaii., left, as wife Linda Schatz, holds the bible and watches at center, during a ceremony in the Old Senate Chamber on Capitol Hill in Washington, Thursday, Dec. 27, 2012. (AP Photo/Susan Walsh)