Most Americans think Obamacare is unconstitutional, and this feeling appears to be about principle -- a plurality say the law has had no effect on their lives. But even if they don't like President Obama's most famous legislation, they like him more than Mitt Romney (by 10 points!). And a huge majority wants to see an arrest in the Trayvon Martin case. Here's our guide to today's polls and why they matter.

Findings: A large number of Americans oppose Obamacare, but it's not clear how many. One poll finds the number to be 47 percent; another says 62 percent of Americans think it's unconstitutional for the federal government to make you buy health insurance.
Pollster: New York Times/ CBS News; Reason/ Rupe
Methodology: Survey of 986 adults from March 21 to March 25; survey of 1,200 adults from March 10 to March 20.
Why it matters: The Supreme Court is hearing epic arguments over the constitutionality of Obamacare this week. It's the president's signature domestic accomplishment, and there is near universal agreement that however the court decides the case, it will have a big impact on the election. The Reason poll also shows how you frame the question matters -- the poll finds 87 percent of Americans say the government does not have the authority to make them buy broccoli. It finds a majority of Americans support the part of Obamacare that prevents insurance companies from denying coverage to people with preexisting conditions -- a requirement the White House says can't survive without the individual mandate, because people would just wait till they're sick to buy insurance.
Caveat: The court can reflect public opinion, but it can also shape it. Also, a Suffolk poll shows a plurality, 40 percent, say Obamacare has made no difference in their lives.

Findings: Obama is ahead of Romney 47 percent to 37 percent; he beats Santorum 49 percent to 37 percent.
Pollster:  Suffolk University
Methodology: Survey of 1,070 likely general election voters from March 21 to March 25.
Why it matters: Many argue that the long Republican primary -- with all the gaffes and prop comedy -- has made voters like the Republican candidates less. Suffolk thinks that's the case, too, pointing out that Romney's unfavorable rating has climbed dramatically while Obama's has stayed the same. The general election matchup is a strong showing for a president given several factors counting against him: An average of 60 percent of Americans think the country's on the wrong track. Obama has an approval rating that's just below 50 percent. And the poll finds that 83 percent of Americans still think we're in a recession, even though it officially ended three years ago.
Caveat: The general election is many months away.

Findings: 73 percent of Americans think George Zimmerman should be arrested for the killing of unarmed teenager Trayvon Martin.
Pollster: CNN/ORC International
Methodology: Survey of 1,014 adults Saturday and Sunday.
Why it matters: Public pressure led to the Sanford, Florida sheriff stepping aside temporarily and a grand jury to be scheduled to start deliberating in April.
Caveat: A backlash to the backlash has begun.

Findings: Americans want more energy options. A majority -- 57 percent -- favor nuclear power, even though the Fukushima nuclear power plant failed only a year ago. And Suffolk finds 78 percent of likely voters want to increase domestic oil production, while 68 percent think clean energy subsidies will help create jobs.
Pollster: Gallup
Methodology: Interviews with 1,024 adults from March 8 to March 11.
Why it matters: We'll be talking about energy a lot this election, it seems -- Romney has taken a page from Newt Gingrich and started arguing that Obama could do more to lower gas prices. Gallup finds Americans think Obama's done a much better job of protecting the environment than crafting good energy policy.
Caveat: Oil prices don't have much direct effect on a president's re-election chances, The New York Times' Nate Silver reports. While higher gas prices hurt the electoral performance of whatever party holds the White House, the affect is small.

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Elspeth Reeve