At first blush, Tim Pawlenty’s endorsement of Mitt Romney doesn’t mean much. Pawlenty hardly caused a ripple when he ran. Nevertheless, the announcement is significant in two respects.

First, Pawlenty knows Rick Perry well from the Republican Governors Association, as do all the current GOP governors — yet today’s decision reminds that none of those governors has endorsed Perry. It’s early, some say, but he apparently didn’t forge close ties with his peers nor command loyalty. They, like other Republicans, are waiting to see if Perry is going to settle down and erase doubts about his electability. Until then, they aren’t going out on a limb. (And they certainly don’t want to be asked if they agree with his take on Social Security.)

Second, Pawlenty’s decision underscores that Perry has not yet been able to corral the GOP establishment and more moderate voters to combine with his Tea Party support. Just as Romney’s “lead” was precarious, one senses that so too is Perry’s. There is, of course, plenty of time for Perry to steady himself and assure non-Tea Partyers, but there is also time to dredge up a Republican candidate who really can unify the party.

Romney has to convince the base that he’s got conservative convictions. Perry’s got to win over those voters whose principal concern is electability and who worry whether he can beat the president. When a moderate governor endorses Perry, or when a respected Tea Party-friendly Republican sides with Romney, we’ll know one of them is gaining ground.