Senate Armed Services Chairman Carl Levin (D-Mich.) acknowledged Monday that Democrats are still searching for a handful of GOP votes to move to the defense authorization measure this week.

“I don’t know whether we have the votes or not,” he told reporters, adding that failing to pass the bill before the midterm elections “would be a major setback.”

Republicans led by Sen. John McCain (Ariz.) are widely opposed to language in the bill to repeal the military’s “don’t ask, don’t tell” policy barring openly gay service members. They have further blasted Democratic attempts to add an immigration provision known as the DREAM Act and another provision to curb the Senate’s use of secret holds to the annual measure, which typically enjoys broad bipartisan support.

Levin railed against those claims and noted that McCain promoted a campaign finance amendment to the defense authorization bill in 2000. “The argument is this has no place on the defense bill, and they’re wrong,” Levin said. “People use the rules here, and they have the right to use the rules here.”

Levin said he had spoken with Sen. Susan Collins (R-Maine) about her concerns unrelated to the series of high-profile amendments, but not about whether she will join Democrats in Tuesday’s procedural vote to move on to the defense bill.

Collins and Sen. Olympia Snowe (R-Maine) are potential swing votes for Tuesday’s procedural motion, although both have criticized Majority Leader Harry Reid (D-Nev.) for attempting to rush consideration of the measure.

Other top GOP targets include Sens. Scott Brown (Mass.) and Lisa Murkowski (Alaska), who has been absent from the chamber since losing her primary election last month. Democratic Sens. Ben Nelson (Neb.) and Jim Webb (Va.) also haven’t indicated how they intend to vote Tuesday.

When the Armed Services Committee voted on whether to add the DADT language to the defense authorization in May, Collins was the only Republican to vote in favor. Nelson supported the amendment, while Webb voted against it.

Gay rights activists have ramped up their efforts in recent days. Members of the Servicemembers Legal Defense Network dispatched representatives and grass-roots supporters to Maine on Monday to apply pressure on Snowe and Collins, while other advocates said a full whip effort was taking place to ensure all 59 Democrats and at least one Republican come together. But the right-leaning group GOProud joined the chorus of Republicans who allege that Reid is using the defense measure for his own electoral gain.

“Harry Reid should stop using gay soldiers as political pawns in a cynical attempt to win votes for his re-election and keep his liberal special interests happy,” Jimmy LaSalvia, executive director of GOProud, said in a statement.