Thousands of abortion opponents marched to the Supreme Court on Monday to mark the 39th anniversary of the Roe v. Wade decision legalizing abortion, and supportive lawmakers urged them to further their cause by working to defeat President Barack Obama in the fall.

The "March for Life" has been held every year since 1974, a year after the landmark Supreme Court ruling. It's consistently one of the largest protests of the year in Washington, although soggy, chilly conditions likely kept this year's numbers down a bit.

House Speaker John Boehner addressed the group, reminding those gathered on the muddy National Mall that he's one of 12 children

"I'm sure it wasn't easy for our mother to have 12 of us, but I'm glad we're all here," the Republican lawmaker said. "I've never considered being pro-life a label or a political position. It's just who I am."

Several dozen members of Congress addressed the rally and were cheered by participants, many of whom carried signs reading "I Vote Pro-Life First," "Defund Planned Parenthood" and "Face It ... Abortion Kills a Person."

Signs endorsing Republican presidential contenders were less ubiquitous, although some in the crowd favored Rick Santorum and Ron Paul, both favorites of conservative Christians.

Rep. Chris Smith, R-N.J., urged anti-abortion voters to unite behind the eventual GOP nominee.

"We don't have the luxury of disunity or nominee disappointment or apathy," Smith said. "For the sake of the innocent, failure to unite is not an option."

Republican frontrunner Mitt Romney has said he wants to see Roe v. Wade overturned. But Janet Hoven, 55, of Chester, N.J., said he still needed to do more to court anti-abortion activists.

"He's going to have to come out very strong for life. I certainly will pray that he will," said Hoven, a Romney supporter.

Carolee Zentkovich, 68, of Columbia Station, Ohio, said she supports Santorum but would gladly vote for Romney in the hopes of getting Obama out of office.

Americans remain strongly divided on abortion.

A Gallup poll last year showed that 49 percent of respondents identified themselves as "pro-choice," while 45 percent called themselves "pro-life." The same survey found that 50 percent of Americans believe abortion should be legal under some circumstances, 27 percent said it should be legal in all cases and 22 percent said it should always be illegal.

Nancy Keenan, president of NARAL Pro-Choice America, said in a statement that politicians supporting the March for Life were ignoring more pressing issues.

"Anti-choice politicians and their allies promised to focus on creating jobs, yet they are attacking a woman's right to choose at near-record levels," Keenan said. "This extreme agenda is out of touch with our country's values and priorities."

Some marchers said opposition to abortion transcends partisan politics.

"Eight years ago, when George W. Bush was president, we were still out here," said Michael Tober, 36, of Muskegon, Mich. "It's not a Republican thing; it's not a Democrat thing. It's a human thing."