Phil Klein calls Mitt Romney’s joint appearance with Donald Trump to accept the latter’s endorsement “the biggest blunder of his candidacy.” I’m not sure I’d go that far, but it’s certainly up there. Consider that last time the effect of a Trump endorsement was polled, by Fox News in Spetember, it came out as a net negative: 31% would be less likely to vote for a Trump endorsee, only 6% more likely.

Those who are working to re-elect Barack Obama are thrilled by the development, touting it on the @BarackObama Twitter account and in a blast email from the Democratic National Committee. Romney will most likely be the Republican nominee, and if Trump says something particularly incendiary, one can certainly imagine an attack ad using the footage of Trump and Romney. But even if this blows over and doesn’t seriously hurt Romney, it’s hard to see how it can possibly help.