With just two major Republican debates remaining before the Iowa presidential caucuses, Donald Trump has been remarkably lucky. The only major candidate who could actually inflict lasting harm on the vulgar poster child for inherited wealth, and the only one who could readily attract and hold some of Trump’s blue collar constituency, is the only one banished — by the idiotic, poll-driven debate rules to which the feckless Republican National Committee acquiesced — from sharing a single stage with The Donald.

For reasons both stylistic and substantive, Pennsylvania’s former U.S. Sen. Rick Santorum could eviscerate Trump in a direct encounter.

This is not necessarily to say that Santorum could vault from near-last to first the way he did for a while in 2012. It is, though, to say he could do enough damage to Trump that either he or another candidate could finally surpass Trump, lastingly, in the national polls.

Here’s why.

The first reason is gumption. Unlike Ted Cruz . and Marco Rubio ., who have studiously avoided (and in Cruz’ case, run away from) all opportunities to engage Trump in a direct and hostile exchange, and unlike Jeb Bush, who just doesn’t project strength, Santorum is feisty enough to stand firm while smart enough to keep the exchange from sounding like a cheap shot.

Think about all the debates Santorum has endured in the past two presidential cycles: Has anybody ever left him looking shaken or beaten? No. While Santorum does not have the knack for the one-liner that remains quotable several days after the event, he also doesn’t allow anyone to kneecap him. He makes his point in a way that always sounds sensible — thoroughly knowledgeable; sincere, not canned; without inconsistencies of internal logic from one argument or issue to the next; and uttered with the force of honest conviction.

Stylistically, he is a perfect foil for the bombastic billionaire. He doesn’t try to speak in soaring rhetoric that sounds either pretentious or choir-boyish (like Rubio) or with trial-lawyerly cadences (like Cruz); he just talks straight, with plain language — and that’s the toughest sort of talk for a verbal bully like Trump to puncture.

Most politicians are like the paper in rock/paper/scissors, trying to cover all eventualities with practiced verbiage. Trump is the scissors, cutting right through their pretensions. But Santorum is the rock, solid and unsliceable.

And one last style point shouldn’t go overlooked: Trump, at 6-foot-3, is a large man who towers over all other opponents but Bush (whose height does him no good because he doesn’t project it). Trump can’t do that to Santorum, also 6’3″ but vigorously younger and, unlike Trump, not prone to energy lulls in-between manic highs.

Style isn’t the only thing giving Santorum an advantage against Trump. His straightforward style merely makes it possible for his vast, vast advantage in substance to gain traction. Trump is, of course, notoriously deficient, not to mention uninterested in, substance. When he can slice an opponent by insults and out-alpha them with bombast, his fans don’t much care about substantive details. But if somebody solid and unyielding engages Trump with arguments in everyman language, expressing an everyman’s concerns, Trump’s mind-boggling ignorance may finally become a real weakness.

Santorum clearly is the most knowledgeable man in every debate. One can easily agree or disagree with his conclusions, but no one can doubt he knows his subject matter not from consultants’ briefing books but in personal, practicable depth.

More importantly, Santorum approaches it all from the palpably genuine perspective of the same blue-collar Americans (or struggling small-business strivers) who are Trump’s political base. Santorum was populist — in a non-demagogic way — before populism was cool in the Republican Party. He always has spoken for the slight underdog who wants a chance to exert the strength he knows he possesses.

Santorum has a history of political successes built on a combination of Ross Perot voters and Pat Robertson voters (to pull archetypes from the 1990s) — two sets that would form a slightly but far from entirely overlapping Venn diagram. Of all the current candidates for president, only Chris Christie can join Santorum in competing with Trump for the Perot set — but Christie, unlike Santorum, offers no stylistic contrast to Trump, but merely represents a paler, portlier version of New Jersey-ish bluster, but with some unattractive prima donna tendencies thrown in.

In sum, Santorum can speak — has always spoken — for the barely-lower middle-income Americans to whom Trump appeals. But his words are real. He doesn’t have a history of, well, screwing the “little guy” the way Trump does. An Iowa pipefitter isn’t likely to relate to Marco Rubio’s gauzy odes to American exceptionalism — but he will recognize a kindred spirit in Santorum’s workaday Pennsylvania instance on America’s true grit.

Santorum alone can dislodge some of Trump’s “Perot voters” and actually keep them — if only he is allowed to stand mano y mano against Trump, where he, unlike the other non-Fiorinas on stage, won’t flinch.

The Republican debate criteria so far have emphasized polls whose indices are notoriously evanescent, rather than prior election results that actually count. It is an embarrassment to the Republican Party that the man who won as many states as any non-nominee since Ronald Reagan, and who won four straight elections as a conservative underdog in a left-leaning state, and who won the first-in-nation caucuses last cycle — and who, to great substantive effect, was the third-ranking Republican in the U.S. Senate — has been kept off debate stages dominated by a quadruple-bankrupted inheritor most famous for Kardashian-style (un-) reality TV.

Rather than limit the next debate stage to six candidates, the RNC should insist that all 11 serious contenders — the ten evanescent poll leaders plus the “defending champion” in Iowa (and Alabama and Minnesota and Colorado, and seven more) — be given the chance to mix it up one final time. If they do, Santorum will be the guy who sends the bully Trump yelping from the arena, nose bloodied and aura finally, fatally destroyed.