Having a presidential primary debate with eight candidates on the stage means no one gets knocked out unless they do it themselves. And no one knocked himself or herself out Thursday night. Instead, several candidates did themselves some good.

Frontrunners help themselves when they meet or beat expectations. Mitt Romney beat them last night, by saying “I'm not going to eat Barack Obama's dog food,” by offering a meaty, punchy response of seven items he would do to get the economy moving again, and by missing no opportunity to emphasize his background as a businessman who knew how to create jobs.

While the coverage emphasized the mini-brawl between former Gov. Tim Pawlenty and Congresswoman Michele Bachmann, the two candidates did themselves more good by what they revealed about their own backgrounds, values, records, and vision. Gov. Pawlenty focused on his achievements as a conservative governor in a purple state; Rep. Bachmann heralded her opposition to President Obama’s policies.

While their attacks on each other were good TV, adding some drama and spark to the debate, they did little damage. Bachmann arguing Pawlenty’s record “sounds a lot more like Barack Obama,” and Pawlenty saying Bachmann’s “record of accomplishment and results is nonexistent,” simply reinforces the views of voters who were already committed to them. It didn’t sway any undecideds.

While the political class has focused much of its attention on the direct confrontation between Pawlenty and Bachmann, it was more important that Iowa voters heard him say, “If you can find Barack Obama's specific plan on any of those items, I will come to your house and cook you dinner,” and heard her proclaim, “I was leading on the issue of not increasing the debt ceiling.”

Newt Gingrich proved again that the counterpunch is often stronger than the punch. Chris Wallace asked the former speaker a tough but fair question about what Gingrich would say to those who felt his “campaign has been a mess so far.” Newt threw a haymaker in response, saying “I took seriously Bret's injunction to put aside the talking points. And I wish you would put aside the ‘gotcha’ questions.” Wallace’s question was legitimate, but Newt successfully evaded it by punching back.

What happens at a debate off stage is often more important than what happens on stage. That was certainly true yesterday for Romney, whose debate performance was bolstered by his tough and passionate response to a left-wing heckler at an appearance earlier in the day at the Iowa State Fair. But the biggest offstage event was Texas Gov. Rick Perry’s very adroit leak Thursday afternoon that he was getting into the GOP presidential race Saturday. It made him a looming presence in a debate he skipped. And it may also have been an attempt to jack up his vote at the Iowa Straw Poll Saturday to create a surprise showing or to obscure a weak one.

In the end, the debate is likely to have little effect on the Straw Poll, the next possible inflection point of the content. For example, Congressman Ron Paul gave a less than stellar performance in the debate, but that didn’t quiet the roar of his well-organized and vocal supporters. While he has no chance of winning the Republican presidential nomination, he may do well at the Straw Poll. Three million people live in Iowa: a couple thousand of them turning up in Ames at the Straw Poll will make any candidate, even a fringe one, a contender.

What really matters Saturday is whether a candidate exceeds expectations. That puts Bachman and Pawlenty in the hot seat. She’s expected to win and he’ll be damaged if he doesn’t “do well,” meaning win, place, or show. And while neither Romney or Perry are contesting the Straw Poll, both could be damaged if the press decides their vote total tomorrow aren’t what the media think they should be. This is especially true for Perry: independent groups are actively working to turn out supporters for the Straw Poll.

We’re still in the political pruning process. Debates like last night’s will become more consequential in the GOP contest the smaller the number of candidates participating. That would allow for more time for each candidate to speak and more consequential exchanges. That’s why we’ll all be watching how the Straw Poll -- and the passage of time and the absence of campaign contributions -- slim downs the Republican field.

Karl Rove is a former senior adviser and deputy chief of staff to President George W. Bush. He is a Fox News contributor and author of "Courage and Consequence" (Threshold Editions, 2010).