ABC News’ Michael Falcone reports:

As he has risen to the top of national Republican presidential polls over the last few weeks, Rick Perry has been forced to confront his past — including the years he spent as a Democrat.

In particular, Perry has been fielding uncomfortable questions about his support for Al Gore in the 1988 presidential race. Perry, who did not switch to the Republican Party until 1989, served as a high-profile Texas supporter of Gore’s presidential bid.

More than two-decades later, as the front-runner for the GOP presidential nomination, Perry frequently cites Gore’s support of the Strategic Defense Initiative, a Ronald Reagan-era anti-ballistic missile proposal that later came to be known as Star Wars.

“I was a Democrat in my days in the Legislature in the 80's and I was under the false idea that somehow or another that conservative Democrats could save the Democrat Party. They couldn’t,” Perry said in an interview with conservative talk show host Sean Hannity on Tuesday. “Al Gore appeared to be the most conservative — a strong Strategic Defense Initiative guy — and frankly we thought that he would be the most conservative Democrat. You, know, we were wrong.”

Last weekend, at a campaign appearance in Ottumwa, Iowa, Perry called Gore a “strong Strategic Defense Initiative proponent.”

But Gore’s support for the Strategic Defense Initiative while he was running for president in the late 1980's was not nearly as enthusiastic as Perry implies.

In fact, just weeks before Gore launched his presidential bid in the summer of 1987, he dismissed the defense proposal as “an electronic Astrodome over the United States” in an interview with the Associated Press.

In a January 1988 interview with Florida’s St. Petersburg Times, Gore was asked whether he would support increasing research funds for the initiative. His response: no way.

“I oppose absolutely any plan for development or deployment of the Strategic Defense Initiative system,” Gore said. “Research on SDI should be confined to a strict interpretation of the ABM treaty. The focus of this research should be to assure that we have a state-of-the-art understanding of the basic science and technology that could be relevant to defense.”

And a few months later, in April 1988, Gore was quoted in the Washington Post as saying that the Strategic Defense Initiative was wrong-headed.

“‘I’m sure that President Reagan sincerely believes he is acting with the best of purposes in looking to SDI as a way to permanently end the threat of mutual nuclear annihilation,” Gore said. “But he is wrong — wrong because SDI is not feasible, wrong because it would entail exorbitant costs and, most important, wrong because it would make the possibility of a nuclear first-strike more likely.”

In the years since, and particularly now that he is a presidential candidate, Perry has taken pains to disavow his past support for Gore, saying that he did not know about the future vice president’s views on the environment. But Perry has continued to use the Strategic Defense Initiative as justification for his endorsement more than 20 years ago.

The Perry campaign declined to comment.