As I wrote yesterday, there are plenty of reasons to be skeptical of national polling early in a presidential primary. But direction does matter. When Fred Thompson’s national poll numbers started diving in 2007 after a splashy entrance, many conservatives figured he was a flash in the pan. Donors recognized that as well. Conversely when Barack Obama started eating into Hillary Clinton’s huge lead in the polls Democrats started taking him seriously, and endorsements and money soon followed.

When Texas Gov. Rick Perry entered the GOP primary more than a month ago, he quickly soared to double-digit leads in all of the national polls. The last three polls — Bloomberg (4 points), ABC/Washington Post (6 points) and Gallup/USA Today (7 points) — show his lead has shrunk considerably.

For comparison’s sake let’s look at the Gallup/USA Today numbers. In August that poll showed Perry with a 12-point lead; now it’s 40 percent lower. USA Today reported: “Romney has been pressing the argument that Perry’s blunt views on Social Security and other issues will make it hard for him to win in November. That may strike a chord: 53% of Republican voters say they would prefer the nominee with the best chance of beating Obama; 43% say they want the candidate who agrees with them on almost all issues. Perry has intensity on his side, however. Seven in 10 of his supporters say they’re more enthusiastic than usual about voting in 2012, while just under half of Romney’s supporters are energized.” In other words the hard-core conservative base really, really likes him, but that’s not enough to sustain his standing.

A Romney backer e-mailed me yesterday: “The idea of Perry — a big-state governor with a conservative reputation — was appealing. The reality of Perry — a candidate with little depth and a troubling history — is not as appealing. Republican voters want to win, and the more information that reaches voters about Perry, the more likely it is that he will come back down to earth.” That’s in large part due to the fact that Perry is playing defense on a variety of fronts and failing to advance his own positive agenda.

But Perry could arrest any erosion and, in fact, reinforce his front-runner status if he did several things. First and foremost, he could stop the nerve-jangling in the GOP by coming out with common sense, effective entitlement reforms. He’d also be showing leadership since his main rivals haven’t done that. Second, he should, while it is still early, start, figuratively, clearing out the garbage littering his path to the nomination. That means addressing financial issues and renouncing silly recommendations in his book (e.g. allowing states to legalize pot). It’s easier to do it now than when his opponents start airing attack ads, as they surely will. Third, he needs to turn in an impressive debate speech in which he has polished answers, not one-liners, to important questions. If he gives another poor performance, the doubts about his candidacy will escalate. And finally, he should stop hiding from the media. Do some Sunday talk shows. Sit down with a national newspaper’s editorial board. Take questions regularly on the stump. If he doesn’t, others will set the narrative.

The fundamental problem for Perry is this: His Texas schtick works with the base (especially in the South) but turns off others, giving rise to an electability issue. As USA Today observes: “Romney does better among the swing voters who hold the key to most general elections. Among all registered voters, Romney edges President Obama while Perry narrowly lags him.” Can he hold the base while winning over less conservative voters? If he can’t do that, as Ronald Reagan, George W. Bush and successful governors such as Bob McDonnell (Virginia) and Susana Martinez (New Mexico) did, he’s not going to be able to convince GOP voters that he can deliver on their fondest wish — defeating Obama in 2012.