Last week, the Family Leader, a conservative pro-family group in Iowa, asked Republican presidential candidates to sign a pledge endorsing traditional marriage and other social issues. Michele Bachmann was the first to say she would sign it. Mitt Romney has decided not to. Tim Pawlenty hasn’t announced his decision.

That tells you something important about the battle for the Republican presidential nomination and the box in which Pawlenty now finds himself. Two months ago, he believed he was in a strong position to break out and become the principal alternative to front-runner Romney. Today he is trying to figure out how to prevent Bachmann from blocking his path.

The decisions on the marriage pledge by Romney and Bachmann were easy because they know their respective constituencies, their strategies and the political imperatives that go with them. Pawlenty’s apparent hesitation underscores the awkward position he’s in and the risks to his candidacy whether he signs or doesn’t.

Bachmann intends to nail down social conservatives and tea party activists and turn them into a force that can propel her to victory in Iowa’s first-in-the-nation caucuses. Success there could enhance her chances of competing elsewhere. Signing the detailed though controversial pledge was an easy decision as a result.

The calculus for Romney was the opposite, but not necessarily more difficult. Neither winning Iowa nor becoming the favored candidate of social and religious conservatives is part of his strategy for capturing the nomination or the presidency. He wants support from those values voters, but, as with others who have won the GOP nomination, he is not willing to pay any price to get it.

Romney has signed other pledges — one not to raise taxes and another to put a cap on spending and support a balanced budget amendment to the Constitution. Romney is all about the economy. But on social issues, he is not willing to lurch too far to the right. He is focused on preserving as much space as possible in which to compete for swing voters in a general election.

Asked about Romney’s position on the pledge, spokesman Eric Fehrnstrom e-mailed back this response: “Mitt Romney strongly supports traditional marriage but he felt this pledge contained references and provisions that were undignified and inappropriate for a presidential campaign.”

Romney’s campaign did not identify the provisions or the footnotes Fehrnstrom cited, but others have raised a number of questions about the document. One provision, which was later dropped, said that, in some respects, black children born into slavery were better off than those born today. Another asked candidates to reject sharia law. Another called for recognition that “robust childbearing and reproduction” is good for the nation.

Family Leader officials are now trying to rebut criticism of their pledge.

That Pawlenty’s campaign is struggling is borne out by recent polls in Iowa (where he is in single digits), by second-quarter fundraising numbers (he raised less than a quarter of Romney’s total) and by the negative narrative that has now attached itself to the former Minnesota governor’s candidacy.

There is perhaps no better sign of how he regards Bachmann’s strength in Iowa than the escalation of his rhetoric over the past week. He first called on Iowa Republicans to think twice about their vote. Being first in the nation, he told Iowans, is more than a privilege, it is a responsibility to take their votes seriously.

“I think it’s important for Iowa not to just be first but to be right, to send a message that the person who wins Iowa is a person who can really be the nominee, who can really beat Barack Obama, who can really be the president of the United States under the most historically difficult and challenging times,” he told an audience in Cedar Rapids last week.

He also derided candidates who just “flap their jaws” rather than get things done.

At that point, Pawlenty still wasn’t singling out Bachmann by name, although the implication was obvious. By Sunday, when he appeared on NBC’s “Meet the Press,” he was no longer so restrained. Asked by host David Gregory about Bachmann, Pawlenty offered a biting critique.

“I like congresswoman Bachmann,” he said. “I’ve campaigned for her. I respect her. But her record of accomplishment in Congress is nonexistent. It’s nonexistent. And so we’re not looking for folks who, you know, just have speech capabilities, we’re looking for people who can lead a large enterprise in a public setting and drive it to conclusion. I’ve done that. She hasn’t.”

Pawlenty is actively working to play down expectations for his performance in the August straw poll in Ames, Iowa, which not long ago he would have been favored to win because Romney is not competing.

In an interview with The Post last week, Pawlenty pointed to a recent survey in the Des Moines Register, which showed Romney and Bachmann topping the field. Pawlenty ran a poor sixth. He said he hopes to show progress by the time of the straw poll, which of course he will, given that Romney and some others are not on the ballot. At this point, Ames is largely a two-person battle between Pawlenty and Bachmann, although Ron Paul could be a factor as well.

Defeat in Ames would be another setback for the former governor, who will need a caucus victory in Iowa next year if he hopes to win the nomination. Pawlenty says that a loss in the straw poll would not be enough to knock him out of the race. His team is confident that, whatever the relative standing of the candidates today, he has more staying power than Bachmann.

Republican strategists partial to Pawlenty believe that Bachmann, given her record and history, could stumble in the months ahead. They hope to profit from any mistakes by the Minnesota congresswoman.

Bachmann fired back at criticism that she lacks executive experience, saying that’s no substitute for supporting the right policies. For the most part, however, she prefers to ignore Pawlenty’s barbs. She is counting on her grass-roots supporters to make a statement for her.

When she opened her Iowa headquarters in suburban Des Moines on a hot afternoon last Saturday, she issued a spirited call for everyone to mobilize for Ames. “How many of you can fill up a car, a bus, a wagon, a train, a sleigh?” she said. “Get your skis on. Get your roller skates on. Get your ice skates on, but get to the straw poll in Ames, Iowa.”

All of which makes Pawlenty’s handling of the Family Leader pledge so telling. His decision will not just show how worried Pawlenty is about the Bachmann threat. It will also will reveal how he sees himself and what kind of candidate he wants to be.