A deepening rivalry over foreign policy between Sen. Lindsey Graham and fellow Republican Sen. Rand Paul burst onto the national stage this week when the South Carolina hawk decided to defend an incumbent Democrat against the Kentuckian’s attacks.

After Paul launched TV ads through his political action committee against three Democratic Senators who are up for reelection this year, Graham leapt into action Tuesday and joined Sen. Joe Manchin (D-W.Va.) on a campaign conference call to dispute the ads’ contention that Manchin’s support for foreign aid to Libya, Egypt and Pakistan is not in the country’s best interest.

On that call, Graham may have made the understatement of the year. 

“Rand Paul’s a good man. I like working with him on entitlement reform, but he has a little different worldview than I do,” Graham said.

But Paul was more direct in his response and questioned Graham’s campaign priorities during an interview with Roll Call. Paul said that while he had well-documented differences with the GOP on some policy issues, he would not take the step of supporting Democrats.

Paul was not swayed by the suggestion that Graham entering the fray in West Virginia doesn’t matter because Manchin is a safe bet to prevail in his rematch with businessman John Raese.

“I think that’s the mental gymnastics to justify why he’s supporting a Democrat in the race,” Paul said.

Though he has not yet signaled an intent to go after GOP candidates, RAND PAC would have no shortage of targets on the GOP side — 30 Republicans voted against the Paul proposal. And Paul took the extra step Wednesday of writing an op-ed for CNN that blasted GOP presidential nominee Mitt Romney’s call to arm Syrian rebels who have been fighting a civil war against the regime of President Bashar Assad, even as Paul argued Romney should be elected president.

Like Paul, Graham has been out stumping for Republicans. He joined Manchin’s conference call from the road in North Carolina, where he was campaigning for Romney.

“I very much would like to have a Republican president, and I would very much like to have a Republican-controlled Senate,” Graham said, “but when it comes to foreign policy and matters of war and national security, I really do try to be bipartisan, and I respect Joe a lot.” 

Graham praised Manchin for taking a serious look at the language Paul proposed before deciding to cast a no vote, accusing Paul of promoting a foreign policy that would help al-Qaida by proposing to require America turn off the aid spigot when terrorists attack embassies abroad. The vote on the Paul proposal came in a late-night session shortly before the Senate recessed for the elections.

Graham has long criticized Paul for proposing a budget resolution that would dramatically slash Pentagon and foreign assistance spending, saying it undermines America’s role in the world.

Foreign aid, Graham said, “is designed to create leverage so we influence the world and not have the world just run us over, and at the end of the day, I believe America should be involved in our national security. We shouldn’t turn over decisions of where we go and what we do to terrorists.”

At the moment, the votes in favor of the sort of engaged foreign policy championed by the likes of Graham and Sen. John McCain (R-Ariz.) have the clear majority in the Senate. Paul, however, believes public opinion is swinging in his direction given the debt situation at home.

“The discussion on foreign policy … within the Republican Party, I think will continue,” Paul said.

While Paul only mustered 10 votes for his measure to strip foreign aid from Libya, Egypt and Pakistan until they meet his conditions, Graham rallied 90 votes for a resolution against allowing an Iranian nuclear weapons program to proceed.

Graham called Paul out on that subject last week in an interview with Roll Call, noting that he was the only one to vote against his resolution, which said that containment was not an option for dealing with an Iranian nuclear weapon.

“When they hear you say if they get a nuclear weapon, we’re not going to use force, that’s exactly what they want to hear,” he said.

Such accusations do not faze Paul, who is also actively opposing intervention in Syria. In his CNN op-ed, Paul wrote, “In North Africa and the Middle East, our problem has not been a lack of intervention. In the past 10 years we have fought two full wars there, and bombed or sent troops into several others. … both parties rush headlong into more places they don’t understand, exemplified Monday by Romney urging action to arm Syrian rebels and topple President Bashar al-Assad.”

In an apparent reference to the uptick in violence against American troops in Afghanistan from Afghan security forces, Paul added, “We’ve been 10 years in Afghanistan and we can’t identify friend from foe. Do you think we can, with certainty, identify friend and foe in Syria?”

Because Paul and Graham are both Republican Senators from Southern states, they could be in the Senate together a long time. After all, Graham succeeded Strom Thurmond, who represented South Carolina in the Senate for 48 years.

The two could continue to trade barbs on international relations and national defense for as long as they stay on the national stage, and if this week is any indication, both seem ready, willing and able to defend their positions.

Steven T. Dennis contributed to this report.