Sen. Tom Coburn failed Tuesday in forcing an up-or-down vote on his amendment ending ethanol tax subsidies, but the Oklahoma Republican succeeded in dealing a blow to anti-tax advocate Grover Norquist.

Coburn fell short of the 60 votes that he needed to limit debate on the measure after Democratic leaders raised procedural objections and whipped against it. But on the 40-59 vote, he succeeded in getting 34 Republicans — including top GOP leaders — to vote for what Norquist has called a $6 billion-a-year tax increase.

After Coburn’s amendment gained considerable momentum in conservative ranks last week, Norquist’s group — Americans for Tax Reform — said Republicans could vote for it only if they also voted for a separate amendment from Sen. Jim DeMint (R-S.C.) that would eliminate the estate tax and ethanol mandates. DeMint’s amendment isn’t guaranteed of a vote and almost certainly wouldn’t pass.

At Norquist’s behest, most Republicans have signed a pledge vowing to never raise taxes or to only support eliminating one tax cut if they replace it with another equivalent tax cut.

Americans for Tax Reform called the vote a “lost opportunity for the Senate to vote on killing the government’s unfair myriad of ethanol preferences.”

But behind the scenes, Norquist’s sway over the Republican Conference is on the rocks, with Senators tiring of his rigid tax-purity test.

Several Senators said Tuesday that they are looking instead to the conservative Club for Growth, which backed Coburn’s amendment as a standalone. Some Senators said that they consider programs such as the ethanol tax credit to be a spending program dressed up as a tax break and that it and other special tax breaks should be eliminated at a time when reducing the deficit has become the top issue.

The ethanol issue will return to the Senate floor on June 24, Majority Leader Harry Reid (D-Nev.) said. Sen. Dianne Feinstein (D-Calif.) will lead the charge because she is the co-sponsor of Coburn’s amendment.

Feinstein voted against Coburn on Tuesday, saying he had used improper methods to force the cloture vote. Traditionally, the Majority Leader is the only person who files motions to end debate. Other Democrats sympathetic to Coburn also voted against him Tuesday for reasons similar to those outlined by Feinstein.