With only days left in the lame-duck Congress, President Obama is pushing hard to accomplish something never before done by a Democratic president: successfully get a nuclear arms-reduction treaty through the ratification process.

White House senior adviser David Axelrod said on "Face the Nation" on Sunday that "the support is there" to pass the New Strategic Arms Reduction Treaty (START) if it comes to the floor. The White House said Friday that Obama is willing to postpone his vacation until the U.S.-Russia pact is ratified.

But it has become clear that Obama is facing a fight over the same issue that derailed President Bill Clinton's quest for a similar accord - missile defense, a cherished Republican goal dating back to Ronald Reagan's presidency. When Republican senators now say they need a fuller debate on the treaty, this is an important part of what they want to discuss.

"Missile defense remains a major point of disagreement between the United States and Russia, and this treaty only makes the situation worse," Sen. John Thune (R-S.D.) wrote recently on National Review Online.

Some Republicans say they want to tweak the Senate resolution of ratification with the goal of then supporting it. Others argue the treaty itself needs amendments which could kill it.

Treaty supporters say the outcry over missile defense is unfounded - and suspect it is a tactic to score political points. They note that there is almost nothing on missile defense in the treaty, which runs more than 300 pages with annexes, and Obama has continued many of George W. Bush's missile-defense policies.

"One of the great ironies is, he made sure there was no way to attack the treaty as being tough on missile defense," Greg Thielmann, a senior fellow at the Arms Control Association, said of Obama. "And yet that's exactly one of the main rationales used by treaty critics."

To Republicans, though, the issue goes beyond the few words on missile defense in the treaty. It reflects their lack of trust in Obama and the Russians and their scars from years of fights with Democrats over the issue.

The Obama administration's policy is "not that radically different from what most Republicans say they want on missile defense," said Stephen Rademaker, a Bush administration arms-control official.

But that simple conclusion "overlooks the long and tortured history of missile defense," he said. "The positions the Obama administration is taking today are not the traditional positions of most Democrats."

U.S. defense officials started considering missile defense as far back as the 1950s. But it was Reagan's ambitious Strategic Defense Initiative, announced in 1983, that turned the issue into political dynamite.

Reagan's initiative, nicknamed "Star Wars," was assailed by Democrats as expensive, unworkable and a danger to global stability. The system envisioned fending off Russia's massive arsenal with space-based lasers and other weapons.