The trouble started in earnest in June. Jeb Bush, relying on nothing but his own hunches, vowed that he’d create 4% GDP growth in his first term as president, thanks to his amazing economic agenda. By his campaign’s own admission, the figure wasn’t based on any policy analysis whatsoever , but Jeb thought it sounded like a nice, impressive number – so it became the basis for his entire candidacy.

It was an annoying, post-policy approach to an important issue, but the problem was exacerbated by the bidding war that followed. Chris Christie said his economic plan would also create 4% growth. Scott Walker – remember him? – said his plan could create 4.5% growth. Mike Huckabee said he’d create 6% growth.

Bloomberg Politics reported this week that Donald Trump wants in on the game.

Republican presidential front-runner Donald Trump revealed a tax plan on Monday that, like many of the proposals put forth by his GOP rivals, contains a dubious assumption: that tax cuts will generate rapid economic growth. […]While Bush assumes 4 percent growth under his plan, Trump said his plan could boost it as high as 6 percent. Leonard Burman, the director of Tax Policy Center in Washington, said a projection of 6 percent growth is “completely implausible.” “It’s faith-based revenue scoring,” Burman said in an interview.

And really, that’s just the start of what makes this exercise so foolish.

Indeed, what these candidates may not realize is the total number of modern presidents – from either party – who saw 4% growth during their tenures. That number is zero. Since World War II, not one U.S. president – not Reagan, not Clinton, no one – has achieved growth that high.

And yet we nevertheless see one GOP candidate after another, insist with certainty that with their tax-cut plans, economic growth will reach unprecedented heights. It’s hard not to wonder why these Republicans believe we should ignore economists and believe tax breaks for the wealthy will spur unprecedented growth, though the answer appears to be, “Because Republicans say so.”

But it’s the lack of seriousness that arguably rankles most. As we discussed in August, each of these candidates are just citing growth projections by pointing to numbers they’ve pulled from their ears. Their arguments can charitably be described as gibberish. I half expect them to start using words like “gajillion” in their stump speeches.

There are plenty of real, qualified economists – some of whom are Republicans – who are more than capable of conducting substantive analyses and offering credible GDP projections. But candidates seeking the nation’s highest office don’t see the point. Why bother with substance when they can throw around made-up figures, assuming primary/caucus voters won’t care about the difference?

What’s more, if the recent pattern holds, there’s nothing stopping other GOP candidates from making up ridiculous numbers of their own. Maybe Rand Paul will promise 8% growth. Perhaps Ben Carson can guarantee 11% growth. Ted Cruz might point to 20% growth and question why the rest of the field lacks true ambition.

It’s all plainly absurd, of course, but if data no longer has any meaning, why not?

P ostscript: Jeb Bush, who released a genuinely bizarre video yesterday touting his made-up number, told Fox this week that he thinks Democrats may want to sabotage the economy on purpose. “I think the left wants slow growth because that means people are more dependent upon government,” the Republican candidate said.