The Obama campaign is putting further pressure on Romney with the video above, released Tuesday, which contrasts him with John McCain, who in 2008 repeatedly denounced personal attacks against candidate Obama. The comparison with McCain may be instructive, but not for the reasons the Obama campaign intends. Yes, the Arizona senator would have denounced the attack. But as Politico reported, the Romney team is working to make sure it doesn't suffer the fate of McCain's campaign, adopting the following mantra: "Whatever McCain did, do the opposite."

Here's how that might play out in this case. Strategists, elites, and cable news types disdain birtherism (for good reason!). And Romney himself has never embraced it. But voters? Although there has thankfully been less polling on the topic since the release of the birth certificate, birther beliefs appear to have remained resilient, barely ticking down in a January poll, for example. Folks who were willing to indulge silly ideas before remain willing to do so now. Without a groundswell of disapproval from Republican and independent voters, why should Romney bother to disavow Trump? McCain would have made the condemnation; the media would have oohed and aahed; and voters would still have voted for Obama. The Donald himself made this argument Tuesday, tweeting, "[Obama] keeps using @SenJohnMcCain as an example, however, @SenJohnMcCain lost the election. Don't let it happen again." For once, the man has a point.

Trump bashers of all political stripes have often reacted incredulously to Romney's intimacy with the mogul, even outside the context of birtherism. After all, is there a single undecided or Obama-leaning voter who will change his or her vote to Romney because an outlandish television celebrity tells them to? Surely not -- but the same logic applies here. If voters are so inclined to disregard Trump, there's no downside: his support won't turn them off Romney, either. On the other side of the balance sheet, the cash that Romney collects at the Vegas fundraiser is perfectly legal tender that can feed the campaign coffers.

Romney's position still isn't quite coherent. For example, as Andrew Kaczynski points out, it doesn't make much sense that Romney leapt to condemn an independent plan to link Obama to Jeremiah Wright -- an attack that is factually defensible, if politically dangerous -- but is willing to indulge birtherism, a belief that is factually and morally indefensible.

All that said, will Romney be able to maintain his po-faced insistence that he is not his fundraiser's keeper? Trump, who is incapable of restraining himself when there's a chance for self-promotion, was doubling (and tripling and quadrupling) down on his statements Tuesday. Perhaps he will eventually go too far -- even for Romney.