One of the most important players in the upcoming 2016 Republican presidential primary contest may be turn out to be a Democrat who died more than 50 years ago.

Campaigning recently at Andover, Mass., Senator Ted Cruz of Texas invoked John F. Kennedy.

“One of the most powerful, eloquent defenders of tax cuts was John F. Kennedy,” Mr. Cruz said, breaking into an impersonation of JFK, complete with a Boston accent. “As JFK said, ‘Some men see things as they ahh and ask why. I see things that never wahh and ask, why not?’”

“JFK would be a Republican today,” Mr. Cruz said. “There is no room for John F. Kennedys in the modern Democratic Party.”

Mr. Cruz returned to the JFK theme later in the same speech. This time his subject wasn’t taxes, but religious freedom. “I gave a speech on the Senate floor in defense of religious liberty. Next to me was a giant poster of JFK … JFK said I will not stand with someone who will not stand with religious liberty.”

Mr. Cruz’s JFK remarks triggered press coverage in the Boston Globe, at Buzzfeed, and at the Washington Post. MSNBC even devoted an entire blog post to trying, lamely, to rebut Mr. Cruz’s argument about JFK, describing it as “ridiculous.”

As the author of JFK, Conservative, I know more than a little bit about this, and I confess it is satisfying to see the argument in the book I wrote surfacing on the presidential campaign trail.

Previous successful Republican presidential candidates, including Ronald Reagan and George W. Bush, have positioned themselves in campaign speeches as heirs to Kennedy, so Mr. Cruz’s comments have a precedent. Back then, too, it drove the left nuts. Said Reagan, campaigning in Warren, Michigan, on October 10, 1984, “Whenever I talk about Franklin Delano Roosevelt or Harry Truman or John F. Kennedy, my opponents start tearing their hair out. They just can’t stand it. Well, of course they can’t because it highlights how far they, the leadership today of the Democratic Party, have strayed from the strength of the democratic political tradition.”

Since it’s become a point of contention, it’s worth remembering some of the details. MSNBC notes that the 65% top income tax bracket Kennedy proposed “is still far higher than today’s 39.6%.” That is true. But it’s also true that Kennedy proposed to lower the top long-term capital gains tax rate to 19.5 percent, which is lower than the 23.8 top rate that now obtains. It’s also true that Kennedy’s Treasury secretary, Douglas Dillon, a Republican, predicted further tax cuts in the future, especially after the Cold War ended.

MSNBC claims the Kennedy tax cut was “rooted in Keynesian economics.” But many Keynesians at the time, from John Kenneth Galbraith to Albert Gore Sr. to Arthur Goldberg, opposed tax cuts, preferring increased government spending to stimulate the economy. If there was to be a tax cut, the Keynesians favored a “quickie,” temporary one that would phase out as soon as the economy improved.

President Kennedy instead favored a tax cut along classic supply-side lines, one that would permanently improve “incentives for personal effort, investment, and risk-taking.”

With his Andover speech, Cruz staked an initial claim to being the Republican best able to carry on JFK’s optimistic, pro-growth policy agenda and underlying vision. He talked about taxes and religious liberty, but there are plenty of other areas where JFK’s legacy is relevant, from the dollar to free trade to welfare reform to foreign policy.

The question as the campaign proceeds will be which other candidates will look to President Kennedy as a source of ideas and inspiration, and whether any of the others will be as vocal about it as Senator Cruz has been. More of this, and by next November even Hillary Clinton may trying to style herself as a John F. Kennedy Democrat.

Mr. Stoll is editor of FutureOfCapitalism.com.