Say what you will about the former speaker, Newt Gingrich. His philosophy, his policy proposals, his track record, his campaign, and all the rest. But the one thing you have to acknowledge about Mr. Gingrich is that he’s a sizzler. He has a way with words. He’s as good a communicator as anyone in modern politics.

In my CNBC interview with Mr. Gingrich this week, he slammed President Obama’s tax-the-rich, class-warfare attack on bank’s and businesspeople. He hammered Mr. Obama, calling him a hard-left radical who is opposed to free enterprise, capitalism, and “virtually everything which made America great.”

It was a brutal, frontal, hard-hitting attack on the president. He called Mr. Obama “the candidate of food stamps, the finest food-stamp president in American history.” He said, “I want to get equality by bringing people up. [Obama] wants to get equality by bringing people down.” He said, “I want to be the guy who says, ‘I want to help every American have a better future.’ [Obama] wants to make sure that he levels Americans down so we all have an equally mediocre future.”

Now, I haven’t heard any of the other GOP candidates offer that kind of response to Mr. Obama’s recent class-warfare speech. Maybe I’m missing something. But I haven’t heard it from Mitt Romney or the others in a sizzle fashion, which is the way Mr. Gingrich operates.

Mr. Romney ought to be beating back Mr. Obama right now. He should at least be asserting that America’s free-enterprise, capitalist system rewards success, not punishes it, and that free-market economics — including supply-side tax-cut policies, worked in the 1920s under Calvin Coolidge, in the 1960s under Democrat John F. Kennedy, and again in the 1980s under Ronald Reagan.

In fact, Bill Clinton joined with Mr. Gingrich in the 1990s to slash the capital-gains tax, cut spending, and enact welfare reform, all of which kept the Reagan boom going. Over 40 million jobs were created in the two decades that followed Reagan’s supply-side tax cut.

Mr. Gingrich made a special point during our talk to reestablish his supply-side bona fides. He said to me, “you’re a witness to this. I was part of [Jack] Kemp’s little cabal of supply-siders.” And then came Mr. Gingrich’s most sizzling point: “You can make an argument that I helped Mitt Romney get to be rich, because I helped pass the legislation.”

So I asked, “Have you ever made that argument to him?” And Mr. Gingrich said, “I am as of right this minute. Just occurred to me.” He went on to say that Mr. Romney “should be thanking me because I did the macroeconomic things necessary to make his career possible.”

This is a Mr. Gingrich putdown of Mr. Romney, is it not? The former Massachusetts governor’s primary attack on Mr. Gingrich is that he spent his whole life in professional politics, and therefore doesn’t understand how to grow the economy and create jobs. Mr. Romney, of course, had a terrific private-sector career at Bain Capital. And he rescued the 2002 Winter Olympics in Salt Lake City. But Mr. Gingrich’s putdown here suggests that without supply-side economic policies, somehow Mr. Romney wouldn’t have succeeded. And that neuters Mr. Romney’s attack on Mr. Gingrich.

Seems to me that Mr. Romney needs to respond to the Mr. Gingrich putdown. And he needs to make his case in the Mr. Gingrich sizzler context.

Years ago, as a rookie running for the Senate against Ted Kennedy, Mr. Romney disavowed Ronald Reagan on a number of occasions. Later on, in 1996, Mr. Romney ran ads attacking Steve Forbes’ presidential run and flat tax. Since then, Mr. Romney has come into the Reagan camp, and that’s fine by me. He also bills himself as a tax reformer. But outside of a corporate tax cut, Mr. Romney has offered no across-the-board tax-reform plan for individuals and small-business owners.

He needs to do this if he’s to fight back against Mr. Gingrich. He needs to reassert his supply-side credentials and clarify his policy path to prosperity.

Please make no mistake. I am not endorsing here at all. I have a high regard for Mitt Romney. What I’m looking for is strong competition for tax-reform ideas. Mr. Gingrich has a 15% optional flat tax. Rick Perry has a 20% plan. Herman Cain had 9-9-9. Jon Huntsman has a strong Bowles-Simpson-type tax reform. But where is Mr. Romney?

Mr. Romney has a good budget-reform program and has endorsed Paul Ryan’s health-care reforms. He has a sound regulatory-rollback strategy. He has moved towards sound money by saying he will not reappoint Ben Bernanke. But at the top of Reagan’s economic-growth plan was an across -the-board tax cut. And it worked.

Republican primary voters are highly supportive of supply-side tax-reform ideas. If Mr. Romney is to stop his slide in the polls and reposition himself as the GOP campaign’s leader, he must respond to Newt Gingrich with a pro-growth tax-reform plan that sizzles.