While Hillary Clinton is slipping in the polls, Rudy Giuliani is on a roll. This is a big swing of momentum. Even the latest Wall Street Journal/NBC poll puts the two frontrunners in a dead heat.

Senator Clinton was hurt badly by her flip-flopping performance in last month’s Democratic debate. America’s mayor, on the other hand, just got a hugely important endorsement from Reverend Pat Robertson. The message to social conservatives is clear: It’s now okay to vote for Rudy.

Why Rudy? Mr. Robertson named out-of-control federal spending, appointing conservative judges, reducing crime, and, perhaps most importantly, “the overriding issue [of] defending against [the] bloodlust of Islamic terrorists,” as issues that strongly favor Mr. Giuliani. On the other hand, he called abortion — something of a sticky subject for Mr. Giuliani — “only one issue” of importance.

The endorsement also suggests that evangelicals are divided on 2008. Indeed, there’s no monolithic movement in favor of any major candidate. This is critical. It means no third-party candidacy from the Christian right.

Recall that Bill and Hillary Clinton benefited enormously in 1992 when Ross Perot swiped 19% of the vote, most of those Republican, in the race against Papa Bush. And when Mr. Perot ran again in ’96, he undoubtedly drained votes from Senator Bob Dole. I note that Mr. Clinton didn’t garner 50% of the vote in either of these elections. But Mr. Robertson has very likely removed this dynamic. No third-party gifts for Hillary in 2008.

Mr. Robertson is a big score for Mr. Giuliani, right when he’s gaining ground on Mitt Romney in New Hampshire. That said, Mr. Romney is still up 15 points in New Hampshire, according to Scott Rasmussen’s poll, and 9.5 points as per the RealClearPolitics average. So you know what? Good for Mr. Romney.

To be very clear, I am not picking sides here. I do think Mr. Romney is running a strong campaign. And he’s gaining strength as a candidate. I also think John McCain is finding his sea legs on the campaign trail. Mr. Romney, Mr. McCain, and Mr. Giuliani are all strengthening what they say and how they say it. But at this writing, Mr. Giuliani appears to be at the top of his game.

When I interviewed him last week on CNBC, it marked the fourth time we had sat down together this year. But something was different. Mr. Giuliani was more in command of a wide breadth of issues, while there was a lot less talk about his considerable accomplishments as mayor of New York City.

For example, when I asked him what a President Giuliani would do to prop up the sagging dollar, he immediately reeled off a series of proposals: Cut spending and stop the earmarks. Deregulate wherever possible. Curb the stranglehold of Sarbanes-Oxley on the securities market. Make sure there’s no new Sarbox for home-loan mortgage credits. Keep the trial lawyers from launching class-action lawsuits against mortgage-security investors, which would only cripple housing credit in the future. Restore confidence in the economy by stopping Charlie Rangel’s mother-of-all-tax-hikes proposal.

That was some list. He also came out for cutting the corporate income tax — both as a pro-growth job creator and as a way to boost the sagging fortunes of the dollar. He’s right on both counts. In particular, he was emphatic about reducing the corporate tax so we can better compete with Europe (read the euro).

Grow the economy. Create more jobs. Strengthen worker wages. Mr. Giuliani was on fire. In fact, at the end of the interview, as we were walking off the set, he confided in me that he would suggest an immediate corporate-tax-cut proposal to President Bush. Mr. Giuliani wants results. And he knows he can win.

“I can beat her,” Mr. Giuliani said. “I can run in key states other Republicans can’t run in. That’s why Democrats are attacking me.”

I still believe that it’s a strong Republican field. And I still believe Mrs. Clinton’s message of heavy spending, middle-class entitlements, and higher taxes is a Mondale-era loser. But there’s no doubt about it, America’s mayor is on a roll.

Mr. Kudlow is host of CNBC’s “Kudlow & Company.”