Debate Looms as a Critical Moment for Santorum The Republican presidential debates have proved critical for just about every candidate in the race - disastrous for some and essential for others. Now it is Rick Santorum's turn. On Wednesday, the four remaining contenders for the right to challenge President Obama will meet again under the glare of the television lights, and under the scrutiny of a nation trying to understand where the Republican contest is headed. The face-off, sponsored by CNN and held in Arizona, one of two states to hold primaries on Feb. 28, will be important for each of the candidates. But none more so than Mr. Santorum, who is suddenly being taken seriously as a threat to Mitt Romney. It is the first debate since Mr. Santorum swept contests in Colorado, Minnesota and Missouri two weeks ago, and it comes as he is under more scrutiny for his background and positions, including his opposition to many prenatal tests and his assertion on Saturday that the government's role in education is "anachronistic." Despite moving to the top of four national polls and several state ones, Mr. Santorum remains a long shot to prevent the well-financed, well-organized Mr. Romney from winning the nomination. Wednesday's debate could change that dynamic. A strong performance by Mr. Santorum, or a particularly weak one by Mr. Romney, could ensure a shocking upset in Michigan, the other state that will vote a week from Tuesday. If that happens, the nomination could slip from Mr. Romney's grasp. Last year, in the run-up to the Iowa caucuses, Rick Perry's debate performances knocked him out of contention. In South Carolina, Newt Gingrich used two debates to become a serious threat to Mr. Romney. A week later, Mr. Romney reclaimed his position by putting Mr. Gingrich in his place in two Florida debates. But the task for Mr. Santorum is not easy. Here are five things that he must do if he wants to emerge from the debate with momentum on his side: Focus on Health Care Senior Republican strategists say Mr. Santorum's most aggressive moments in the debates so far have been when he criticizes Mr. Romney's health care plan as governor of Massachusetts. He has been relentless in accusing Mr. Romney of being the inspiration for Mr. Obama's health care overhaul. During one debate in Florida, he had Mr. Romney stammering. If he can do that again, it will be a good moment for him. Look Presidential When Mr. Santorum was at 2 percent in the national polls and hardly seemed to be a threat, he could afford to come across a bit like a fringe candidate. He cannot anymore. Voters in Arizona, Michigan and 11 Super Tuesday states will be watching closely on Wednesday, and they will be trying to determine whether they can picture him in the Oval Office. Mr. Santorum will no doubt try to rise above the mudslinging that has characterized much of the race, in part as a way of conveying that presidential quality. But Mr. Gingrich and Mr. Romney will be doing everything they can to keep him engaged. Rattle Romney One of Mr. Romney's great strengths throughout most of the debates, and for much of 2011, was his calm, cool demeanor. He rarely got rattled and conveyed a sense of stature that voters tend to like. But there have been times when his rivals have gotten under his skin, and those have tended to be his worst moments. Mr. Perry did it on immigration in an early debate. And Mr. Gingrich did it on taxes and Bain Capital in South Carolina. The question for Mr. Santorum is whether he can find a way to do it without coming across as mean. One of Mr. Santorum's strengths with voters is that he remains likable. If he can get Mr. Romney to lose his cool without seeming like a bully, it will help him in the coming primaries. Be Authentic If elections are about presenting voters with contrasts, this may be Mr. Santorum's ace in the hole. With Mr. Romney sometimes seeming calculating about his positions, Mr. Santorum seems that much more real. But it is easy to be authentic when you are at the bottom of the pack, with no one thinking you can actually win. The challenge for Mr. Santorum is to make sure that the possibility of success does not make him come across as somehow less genuine - like a typical politician. Avoid Gingrich and Paul Most of the focus on Wednesday will be on the matchup between Mr. Romney and Mr. Santorum. But the two other candidates, including Ron Paul, will be on the stage, and they will be eager to knock Mr. Santorum down as well. Mr. Gingrich, in particular, has a sharp wit and an ability to harness the enthusiasm of the audience. If Mr. Santorum is not careful, it could be Mr. Gingrich who sets a trap for him.