WASHINGTON -- Wisconsin Democrat Russ Feingold was one of the Senate's leading voices on foreign policy while in office, opposing the Iraq War and calling for a withdrawal from Afghanistan long before it became popular to do so. He served on the Foreign Relations Committee and had an extensive foreign policy agenda. And now that Mitt Romney has selected Rep. Paul Ryan (R-Wis.) as his running mate, he's concerned with the lack of foreign policy readiness on the GOP presidential ticket.

"The Romney-Ryan ticket is extremely weak when it comes to foreign policy," Feingold said in an interview with The Huffington Post. "These guys do not have a serious view or background in what's going on in the rest of the world. This is extremely important in a president and vice president."

Romney's top surrogates have been rushing to defend the ticket's foreign policy chops.

On Sunday, Sen. John McCain (R-Ariz.), another foreign policy heavyweight in the Senate, compared Romney's experience to Ronald Reagan's and criticized President Barack Obama's international agenda. Still, he had trouble coming up with foreign policy accomplishments for Ryan, simply noting that his budget policies would prevent deep cuts to the Pentagon under budget sequestration.

"I think that Mitt Romney understands our nation's challenges," McCain said on "Fox News Sunday." "He's proven that by the proposals that he's put forward, his understanding of the importance of our relationship with Israel -- which has hardly ever been worse -- his understanding of American exceptionalism, which President Obama has abandoned."

"And I think that when you look at Congressman Ryan's experience," McCain added, "his proposals ... prevent a sequestration from taking place. And finally, the vice president of the United States has been wrong nine times out of 10 on every major foreign policy issue and challenges that we faced."

Former GOP presidential candidates Newt Gingrich and Tim Pawlenty similarly defended Romney and Ryan on Sunday. Gingrich said it was "an advantage that they’re not part of the current mess," and Pawlenty argued they "have a terrific national security policy team around them."

"A country that wants to be safe and protect itself from the threats ... around the world should not go with two people who really don't seem to care or find it interesting to deal with those issues at all," said Feingold, regarding Romney and Ryan.

"They are almost exclusively focused on what they call economic issues; what it is really is protecting the wealthy," he added. "This is not a team that is really ready to lead the country internationally."

On Afghanistan, Romney's policy has been a bit of a mystery even to his supporters, with top GOP senators unable to explain what his plan is.

While abroad recently, Romney was the subject of a series of embarrassing headlines, after he insulted the British on their preparation for the London Olympics and made comments about Palestinian "culture."

"His trip was very narrow in terms of the places he visited," said Feingold. "A lot of our challenges in the world come from places like the Middle East and Africa and Asia. ... What about showing some seriousness and purpose about places that are really among the most challenging? We have a pretty good relationship with England and Israel. Of course, they are among our best allies. But that isn't a serious attempt to pursue foreign policy around the world."

When asked for comment, Romney campaign spokeswoman Andrea Saul argued that Romney would be stronger on foreign policy than the current administration, which has "weakened our country at home and our influence abroad."

Obama "thinks visiting our closest ally in the Middle East is a 'distraction,' that Hugo Chavez is not a 'serious' threat, and that the right response to Russia is to promise more 'flexibility' in exchange for giving him 'space' before the election," she said in an email. "Here at home, 23 million Americans are struggling for work while more people are in poverty than ever before. Gov. Romney understands the difference between our allies and those who will challenge us and has the proven leadership we need to get Americans back to work and jumpstart the economy."

Under Wisconsin law, Ryan is allowed to keep his name on the ballot for reelection to his House seat in the state's first congressional district while running for vice president. In an interview with CBS's "60 Minutes" on Sunday, Ryan said he planned to take advantage of this provision. If he wins as vice president and reelection to the House, Wisconsin will hold a special election to replace him in the district. Joe Biden also stayed on the ballot for Delaware's U.S. Senate seat while running in 2008.

Feingold said it was time for Ryan to give up his House seat if he was serious about running for vice president.

"If this guy thinks he should be vice president, and he's ready to be president, he shouldn't have to wear a belt with suspenders," he said. "He should pursue that and let the people of the first congressional district pick a new congressman. I really feel he should give that up."

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