JFK was no free marketeer, but his 1963 tax cut did stimulate the economy for a considerable enough spell. Even Barry Goldwater acknowledged as much, writing in his memoir With No Apologies, though Goldwater had also said his only objection to the Kennedy tax cut was that it wouldn't stimulate the economy without concurrent federal spending cuts.
Which we see today, or will soon enough. The recent tax cuts did put a jump into the economy but without substantial federal spending cuts and with the effects of the tariffs (three guesses who really ends up paying for the increased costs tariffs end up inflating, especially when there's more federal spending to favour those select few whom Washington deems worthy of "aid" to offset the effect) it can't be sustained. It'll come soon enough to the point where we think it was a nice tax cut while it lasted. Because when it comes to federal spending, Washington is still partying like it's 1999 . . .