Republican presidential hopeful Rudy Giuliani addressed his Democratic past on Tuesday and offered one reason for his political conversion — the economy and taxes.

"I don't think anything separates us more right now between Republicans and Democrats than how we look at taxes," the former New York mayor said. "What we understand as Republicans is that, sure, the government is an important player in this, but we are essentially a private economy. What Democrats really believe ... is that it is essentially a government economy."

In the days of President Kennedy, Giuliani said, Democrats understood the concept of the private economy and cutting taxes. But, he said, Democrats have "kind of lost that."

"It's one of the reasons that I used to be a Democrat and I'm now a Republican," Giuliani said before quoting Winston Churchill as saying: "If you're not a liberal when you're 20, you have no heart, but if you're not a conservative by the time you're 40, you have no brain."

The line prompted laughter from Giuliani's audience, a few hundred people affiliated with the Hoover Institution, a public policy center.

As he seeks the Republican nomination, Giuliani faces the challenge of winning over conservatives who make up the GOP's base and view him skeptically because of his moderate views on social issues and his past allegiance to the Democratic Party. In 1994, Giuliani endorsed Democratic Gov. Mario Cuomo over Republican challenger George Pataki.

Addressing his political about-face, Giuliani said he once was a Democrat, then spent five years as an independent before finding a home with the Republican Party.

"Ronald Reagan made only two changes. I was like Churchill, I made three," he quipped.

Turning serious, he said he struggled with his political identity while he was an independent.

"I would say to myself Democrats care about the poor and Republicans don't, and how can I join the party that doesn't care about the poor," Giuliani said. "I finally came to the conclusion that we care about the poor more."

Later, when questioned on whether he had the foreign policy credentials to be president, Giuliani sought to diffuse another potential stumbling block to the nomination.

"What makes you think that the mayor of New York City doesn't need a foreign policy?" Giuliani asked, as the crowd laughed and applauded.

Turning serious, he said he traveled the world extensively since being out of office and grasped foreign policy issues while mayor in the 1990s.

"It's something that I think I know, I think I know as well as anybody else who's running for president, probably better than a lot," Giuliani said.