WASHINGTON — As many as 50 million Americans are expected to tune in tonight for the first face-to-face debate between President Barack Obama and Mitt Romney, his Republican challenger.

Historians suggest that televised debates rarely decide a presidential election. But memorable one-liners (Ronald Reagan’s “There he goes again”), uncouth mannerisms (think a sweaty Richard Nixon or a sighing Al Gore) and long-winded, wonky answers can shape public perception.

The first of the three presidential debates will be about domestic affairs but expect both candidates to try to bring up other issues to make themselves look good and the other guy look bad. Here’s an (unscientific) list of things to watch out for in Round 1 of Obama vs. Romney:

Obama

* Playing it safe: As the front-runner, Obama has the most to lose by coming off as too aggressive or unveiling potentially controversial initiatives. He also appears to score higher than Romney on the always-important “likeability” index. For those reasons, many observers believe the president will play on the safer side yet defend his record against the inevitable attacks.

“I think his challenge, first of all, is to protect his lead,” said Alan Schroeder, a professor of journalism at Northeastern University and author of “Presidential Debates: 50 Years of High-Risk TV.”

“So this may not be the opportune time for big, bold departures from what he has said previously.”

* Tax cuts: Congress punted on whether to extend tax cuts for pretty much all Americans (Republican plan) or only those making less than $250,000 a year (Democratic and Obama plan). Expect to see Obama continue his mantra that Romney would cut taxes for the rich and enact a budget plan that raises taxes for the middle class.

“Meanwhile, there has been very little scrutiny of President Obama’s tax plan … and hopefully Romney will ask questions about it,” said William McBride, chief economist at the conservative Tax Foundation.

* Obamacare and Medicare: The president will likely have to defend a health reform law that remains unpopular with many Americans. At the same time, voters appear hesitant to embrace major changes to Medicare and Medicaid as advocated by Romney and running mate Paul Ryan.

Overall, Brookings Institution senior fellow Henry Aaron believes the advantage goes to Obama. “Romney is in a difficult position of having been for it before he was against it,” Aaron said of Romney’s support of similar health care reforms while Massachusetts governor. “I think there is a lot of confusion with respect to where Mitt Romney is on Medicaid and Medicare.”

* Jobs, or lack thereof: Moderator Jim Lehrer is certain to ask the president about the lingering high unemployment rate and lackluster job creation numbers. It’s been the central theme of the Romney campaign thus far, so expect Obama to be on the defensive as he attempts to convince Americans how much worse it could have been without his administration’s actions.

“His goal will be to raise the number of voters who blame Bush, not him, for our economic circumstances,” Frank Donatelli, chairman of the Republican organization GOPAC and part of several past presidential debate-preparation teams, told Politico recently.

* Demeanor: Although great at the stump speech, Obama can be long-winded and prone to getting lost in the weeds when it comes to policy. That’s a habit his debate team is trying to break. At the same time, expect the president to try to come across as assertive yet cool under Romney salvos.

Romney

* Playing hardball: Trailing in the polls, Romney is expected to be on the offensive for much of the debate, especially when it comes to the president’s job creation record. Of course, being too aggressive has risks, too. But Northeastern’s Schroeder said this is Romney’s chance to “make the sale.”

“This is his best opportunity to try to keep the debate centered on the president’s record and try to be on the offensive as much as possible,” Schroeder said.

* Jobs and the economy: An oft-repeated critique of the Republican nominee is that he has been long on criticizing Obama’s economic record but short on outlining his own specific strategy. Expect to hear plenty of facts and figures (43 months of unemployment above 8 percent, etc.) but perhaps more specificity on how he would bring his businesses skills to the Oval Office.

“There has to be a contrast between a Romney recovery and Obama stagnation,” former Republican House Speaker Newt Gingrich and Romney rival recently told “Face the Nation” on CBS. “You first have to make sure people say, ‘Yeah, Obama’s stagnation is unacceptable,’ but then you have to say, ‘by the way, the better guy will be Romney.'”

* 47 percent: Romney will have to address his secretly recorded comments on the 47 percent who he says are overly dependent on government because, even if Lehrer doesn’t bring it up, Obama surely will. One likely answer: too many Americans need food stamps and government support because of the Obama administration’s failure on the job creation front.

* Foreign policy: Foreign policy is on the agenda for the second and third debates, but Romney may attempt to bring up it on Wednesday. He has been hammering the president on the administration’s relationship with Israel, its policies toward Iran and security concerns in the Middle East.

“I think if it hasn’t been on the minds of voters, it should be especially after the Sept. 11th attacks (in Benghazi, Libya),” said James Phillips, senior research fellow for Middle Eastern Affairs at the Heritage Foundation.

* Demeanor: Observers said Romney will also have to overcome the Democrats’ characterization of him as an aloof millionaire out of touch with most Americans. Republicans attempted to counter that narrative throughout the Republican National Convention in Tampa with stories about Romney’s charitable works, his family and his religious beliefs.

But Romney has also been stressing that the debates are about much more than the personalities of the players and who lands the best punches.

“It’s about something bigger than that,” he said in Denver on Monday night. “These debates are an opportunity for each of us to describe the pathway forward for America that we would choose.”

Kevin Miller — 317-6256

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