The Senate soundly rejected a constitutional amendment outlawing same-sex marriage Wednesday, forcing social conservatives to refocus their efforts on defeating lawmakers who opposed the measure.

A procedural vote on the bill failed by a 48 to 50 margin, but despite the lack of success at even gaining a simple majority on the measure, supporters claimed victory.

“I think it is a great start,” said Sen. Wayne Allard (R-Colo.), who acknowledged that opponents of the bill could also claim victory if they focused solely on the vote total.

“If they technically want to make that argument I guess they can on the number of votes, but I think it is a win,” he said.

The legislative battle now moves to the House, where a vote could be held in September. And a broader political battle over the issue is expected to begin immediately outside the Beltway, as supporters of the same-sex marriage ban try to defeat Senators who opposed the measure, or at least pressure those Senators to offer an iron-clad guarantee that they will support a constitutional ban if it again arises.

“The political moment now for a lot of supporters is to make sure every incoming freshmen Senator is for a constitutional amendment,” said a Senate Republican leadership aide. “They want to make sure folks are on the record clearly that they will vote for that amendment.”

Jim Backlin, vice president of the Christian Coalition of America, said his group and others would spend the August Congressional recess trying to pressure the Senate to vote again on the issue in September.

“We feel that this particular vote will energize the evangelical Christian community,” said Backlin, who added that the religious community would focus their efforts on “Senate races, House races, and the presidential race.”

But Democrats said they are not worried about facing the wrath of some voters, and argued that most people are more concerned about domestic and foreign-policy issues that affect them directly.

“I don’t doubt there are elements of our society that feel impassioned on this issues, both sides, but I think the vast majority of Americans are interested in things that impact their lives,” said Sen. Jon Corzine (N.J.), chairman of the Democratic Senatorial Campaign Committee.

A senior Democratic aide was more blunt in assessing the vote, calling it “a huge embarrassment for the Republicans.”

“They are not getting any traction out of it,” the Democratic aide said. “To the contrary, it is backfiring on them from big cities to small towns across the country.”

The House will likely vote next week on a “DOMA Defense” bill — a measure that would prevent federal courts from hearing legal challenges to the Defense of Marriage Act. During Wednesday’s floor votes, the GOP leadership conducted a whip check for both the DOMA bill and for a amendment barring gay marriage.

The whip check on the constitutional amendment does not mean a vote is imminent. Republican leaders are aware that the issue is a divisive one and want feedback from Members on the subject.

“The leadership wants to go into the August break with a sense of where we are,” said a senior GOP aide. “We also want to watch how Senators are treated when they go home.”

At Wednesday morning’s Republican Conference meeting, staff were kicked out of the room midway through the session so that lawmakers could share their views on the gay-marriage issue with a reduced fear of press leaks. One Member who was present likened it to an “open mic” session and said that there were speakers both for and against a constitutional amendment.

Lawmakers said they got the impression from Wednesday’s Conference meeting that the leadership was aiming to bring an amendment to the floor in September.

During his regular weekly session with reporters, House Majority Leader Tom DeLay (R-Texas) said, “I think it could very well come up this year.”