The fact that Barack Obama in 2008 got through his Democratic nomination battle with Hillary Clinton is offered as proof of the point. But that's like comparing a pillow fight between two kids in pajamas and a rerun of Rocky Balboa vs. Apollo Creed.
In 2000, the GOP primary fight between George W. Bush and John McCain was no day at the beach. However, Bush's smears of his opponent in South Carolina that year were more in the nature of innuendo compared to the open accusations of lying and influence peddling now being swapped by Gingrich and Romney. McCain in 2000 swallowed his pride then and grudgingly endorsed his assailant in the general election, but the scars remained to discerning eyes long afterward.
The notion that front-running Romney and the Republican Party will be strengthened by this year's mudslinging is extreme wishful thinking. It requires, for one thing, a pipedream that independent voters with no allegiance to what is still called the Grand Old Party will flock to its standard in November.
The Republican primary marathon has already gone on long enough to cast the party of Lincoln and of Reagan -- he of the 11th Commandment, "Thou shalt not speak ill of another Republican" -- as prone to unruly and irresponsible political hackery bent on winning at any cost.
The frequent barrages of personal slanders aired in the seemingly endless series of televised candidate debates have come to dominate the campaign narrative. The serial debates serving up venom and flashes of personal hostility have come close to overshadowing the one remaining unifying objective of all the contenders and Republicans in Congress -- to drive Barack Obama from the Oval Office.
Romney's tactical mistake in delaying the release of his income tax returns provided Gingrich the opportunity to pounce, not only on their contents but also on his opponent's recalcitrance in making them public, implying Romney had something more to hide.
The ammunition provided to the Obama campaign by Romney's damaging gaffe and Gingrich's exploitation of it certainly will be used in the fall campaign if Romney is the Republican nominee. The former Massachusetts governor's acknowledgment that over the last two years he paid only about 15 percent in capital gains on his investments is a gift on a silver platter to the president's re-election aspirations.
It's a revelation that dovetails nicely with Obama's call for "the Buffett rule" requiring millionaires and billionaires like Warren Buffett to pay more in taxes than his now famous secretary. Trotting her out in Michelle Obama's box in the House gallery during the State of the Union address was Exhibit A of the Obama campaign's plans.
Romney's great personal wealth, another Gingrich target, also adds fuel to the Democratic assault on growing income inequality through financial manipulations, spotlighted by the Occupy Wall Street movement. Romney has become the personification of the "1 percent" the protesters rail about.
Furthermore, Gingrich's declaration of intent to stay in the Republican race for the nomination all the way to the party's national convention, if carried through, can only deepen the ill will created by the intensely personal nature of the Gingrich-Romney slugfest. And it promises even more fodder for the Obama campaign the longer it goes on.
Republicans who console themselves that their party's circular firing squad will make the surviving candidate stronger for the fight with Obama ahead must be smoking a prohibited substance.
(Jules Witcover's latest book is "Joe Biden: A Life of Trial and Redemption" (William Morrow). You can respond to this column at firstname.lastname@example.org.)