On August 16, shortly after he jumped in, he led by 11. Today it’s down to four nationally and a dead heat in Florida, where Romney spent the day ferociously attacking him on Social Security and, er, … jobs.

Most ominously, perhaps: His favorable rating is down in multiple polls since the first debate.

Mr. Perry’s numbers have been in net-negative territory in four polls released since the first debate, however. On average, 27 percent of respondents held a positive view of Mr. Perry in these polls, while 38 percent held a negative one.

Although few of these pollsters provided a partisan breakdown of their results, Mr. Perry’s numbers do not appear to have declined appreciably among Republicans. So one can infer that the movement has probably been caused by independent voters and Democrats.

The trend of the past few weeks may or may not be indicative of their future trajectory. Nevertheless, of voters who have formed an opinion of Mr. Perry so far, almost 60 percent in post-debate polling hold a negative view…

It seems possible that if Mr. Perry is the nominee and if economic performance continues to be sluggish, we could wind up with an incumbent president whose disapproval rating is at or above 50 percent matched up against a Republican opponent whose unfavorable rating is also in the 50s.

That’s gold for Romney’s electability argument, although he’s not resting on that. Here’s the e-mail he dropped on Perry this a.m.:

Rick Perry released a web video this morning that called President Obama “President Zero,” a reference to the zero jobs created in August. Now the Romney campaign has blasted out an e-mail dubbing Perry “Governor Sub-Zero.”

“In his campaign’s latest video, Governor Perry criticizes President Obama for an economy that added zero jobs in August, yet Texas added even fewer and has over a million people unemployed,” said Romney spokeswoman Andrea Saul in a statement. “This election is about choices – and voters will have the opportunity to choose between Mitt Romney, a conservative businessman, or Rick Perry, a career politician whose own state’s unemployment rate has doubled on his watch and is the worst in the region.”

Translation: Perry might be worse for the economy than Obama is. Perry’s team unloaded on Romney’s own jobs record in response and then replied to Mitt’s Social Security attacks by basically calling him a Democrat, but this dynamic captures Perry’s problem over the last three weeks — he’s constantly playing defense. Against … Mitt Romney. Presumably that’s strategic, aimed at signaling that he’s the “big hoss” in the race by letting the rest of the field buzz around him with attacks, but there’s no evidence that it’s working. For the supposed cowboy in the field, he sure is passive. Tomorrow night he needs to pull that six-shooter and start firing away at RomneyCare. Or is that no longer an issue for anyone?

Exit question: Did Romney actually accuse unnamed other candidates of “being phony and … pandering to an audience” today in Florida? Really? Mitt Romney?