A similar ban passed the House last month, and Senate Democrats quickly pronounced it dead on arrival in their chamber. It is almost certain to be defeated there, and even if it were not, President Obama would veto it. But backers of the ban are eager to bring to the floor of the Senate the same impassioned debate over abortion that has been taking place in state legislatures around the country.

But what is bringing all these marquee political names together is not the Iowa State Fair or a Tea Party rally on the National Mall. Rather, they are all talking about how to advance a bill in the Senate to ban abortion at 20 weeks after fertilization.


Plans under discussion among the staff members of a handful of Republican senators and antiabortion groups would involve bringing the measure up for a vote, probably as part of debate over a spending measure, sometime after Congress returns from its August recess. Because of the Senate’s porous rules for introducing amendments, people on both sides of the issue say they believe a vote is more than likely if the legislation comes together.

“I think there’s significant support across the country for the idea that after 20 weeks, abortion should be significantly limited,” said Rubio, who has taken a leading role in trying to generate support for the bill. “Irrespective of how people may feel about the issue,” he added, “we’re talking about five months into a pregnancy. People certainly feel there should be significant restrictions on that.”

Republicans are hardly unanimous about the wisdom of entangling themselves in a national battle over abortion rights; many believe that the party should remain focused on addressing economic issues and fighting Obama’s health care overhaul.


“I’m focused on energy, the economy, and what’s happening with the president’s health care law,” said Senator John Barrasso of Wyoming, a member of the Republican leadership. Asked whether he thought abortion was a distraction for his party, he stuck to a popular Republican refrain: “I’m completely focused on jobs, the economy, the health care law.”

Democrats, meanwhile, are wary of the damage that a “no” vote on second-trimester abortion restrictions could inflict on some of their more vulnerable senators up for reelection in 2014, particularly in Arkansas, Louisiana, and North Carolina, where legislatures have recently imposed strict limits. On Friday, the governor of North Carolina said he would sign into law new regulations on abortion clinics.

“I’ve taken a lot of tough votes,” said Senator Mary L. Landrieu, a Democrat of Louisiana, who added that she doubted she could support a ban at 20 weeks. “That’s what I’m here for, to take votes. And if we have to take it, we take it.”

The success of new limits on when, how, and where abortions can be performed has helped invigorate the Republican base like few other issues this year. Because of such intensity, antiabortion groups say they have found considerable interest among the newer generation of Republican senators, especially those seeking to build up — or, in some cases, repair — their standing with conservative voters.

Some see even broader appeal. Even though the issue of reproductive rights has been problematic for Republicans — who have been repeatedly embarrassed by comments from politicians who come off as sexist or ignorant of science — those who support 20-week bans say the dynamics of this debate are different.


And some conservatives see this as the only winning social issue they have left in their political arsenal. Unlike same-sex marriage, which has steadily gained support, recent polls have shown that the public believes that abortions later in pregnancy should be restricted.

Antiabortion activists said that after the recently approved House measure and success in states like Texas, which approved a 20-week ban this month, they saw an opportunity they could not pass up.

Drafting a bill, however, will require conservatives to resolve a fundamental disagreement: how to find constitutional justification for a nationwide ban despite their reservations about giving the government broad regulatory powers.