Republicans weighing a White House bid fiercely oppose a new nuclear arms treaty with Russia and stand in stark contrast to two presidents, Democrat Barack Obama and Republican George H.W. Bush, on a critical foreign policy issue.

"It's an obsolete approach that's a holdover from the Cold War and a bilateral treaty without taking into account multilateral threats," former House Speaker Newt Gingrich said Wednesday, becoming the latest potential 2012 candidate to object to swift passage of the treaty without changes.

Gingrich joins Mitt Romney, Tim Pawlenty, John Thune and Sarah Palin — all outspoken critics of the pact. The bright line between would-be GOP challengers and the incumbent Democrat raises the likelihood that the New START treaty will become a 2012 issue and its success or failure will reverberate as the next presidential campaign takes shape.

On the treaty, potential candidates are to the right of several prominent Republicans, including former Secretary of State Condoleezza Rice and Sen. Richard Lugar of Indiana, an arms control expert and the top GOP lawmaker on the Foreign Relations Committee.

Bush gave the treaty's prospects a potentially significant boost Wednesday, saying, "I urge the United States Senate to ratify the START treaty."

The likely candidates' far-right positions on a major national security issue may play well in the Republican primaries where conservatives dominate. But the stances could make the eventual GOP nominee's pitch harder come the general election, when swing voters will be critical.

Obama, conversely, is making moves that could appeal to independent voters.

He's working across the aisle with Republican leaders in Congress to ensure that before lawmakers leave Washington for the holidays, the Senate ratifies the treaty he signed with Russia in the spring. The president also has indicated that the treaty is a higher priority than other issues his Democratic base cares about, including immigration reform and allowing gays to openly serve in the military.

Republican presidential hopefuls have weighed in on the treaty as Obama put its ratification high on his wish list for Congress' lame-duck session.

Among their arguments against it: The treaty would limit missile defense as well as hamper the U.S. nuclear and conventional weapons programs while giving Russia too much leeway. Several have called for the White House to wait until the new Congress convenes in January, when the GOP boosts its numbers in the Senate. That will make it tougher for Obama to get the 67 Senate votes necessary for ratification.

"Why the hurry, Mr. President?" Romney, the former Massachusetts governor, asked last week in a Boston Globe column. "A treaty so critical to our national security deserves a careful, deliberative look by the men and women America has just elected."

In a column published Thursday on National Review's website, South Dakota Sen. John Thune wrote that "New START misses one opportunity after another to maintain a stable nuclear relationship between our two countries." He, too, objected to Obama's insistence that it pass this year, saying: "This flawed treaty has too great an impact on America's national security to be taken lightly or rushed for the sake of political pride."

Also, Minnesota Gov. Tim Pawlenty objects to the treaty in part because "it's premised on the dangerous and naive belief that cuts in our nuclear weapons will somehow discourage proliferation by other regimes, when in fact the exact opposite result is more likely."

Although no Republican has formally entered the race and the election is still two years away, potential candidates are seeking to demonstrate their foreign policy chops to prove they can preserve the GOP's perceived advantage on national security issues.

"This will be a big issue because as a consequence of this treaty, President Obama will continue to undermine missile defense," Gingrich said in an interview with The Associated Press.

Obama insists the New START treaty aimed at reducing nuclear weapons in the U.S. and Russia is a "national security imperative."

The treaty calls for the destruction of hundreds of old nuclear weapons, relics of the Cold War, and a system for each country to verify the other has reduced its stockpile as promised.

Polling shows the public is on Obama's side. A recent Associated Press-GfK poll found that two-thirds of Americans believe the Senate should ratify it. Besides a strong majority of Democrats, supporters include more than six in 10 Republicans.

The opening 2012 salvo on the matter arguably came in April, when Obama was in Prague to sign the treaty with Russia.

Palin, the former Alaska governor and 2008 vice presidential nominee, created a stir by criticizing Obama — and suggesting he was weak on nuclear defense — while he was overseas.

She expressed outrage over a provision that says the U.S. could launch a potentially devastating conventional military strike, but not a nuclear one, if a non-nuclear state were to use chemical or biological weapons against the U.S. or its allies. She likened Obama to a kid poised for a playground fight who said: "Go ahead, punch me in the face and I'm not going to retaliate. Go ahead and do what you want to with me."

That spurred an intercontinental tit for tat with Obama — and set the stage for more Republican hopefuls to object to the treaty.