When George W. Bush asked Congress for the authority to attack Iraq, New York Congressman Amo Houghton voted no. He voted against several of Bush’s tax cut schemes, too, and against the Administration’s proposal to drill for oil in the Alaska National Wildlife Refuge. Houghton has long argued that the United States must make a greater commitment to work with the United Nations and has been an enthusiastic supporter of the International Criminal Court and other multilateral initiatives. He supports abortion rights, gay rights, consumer protections and expansion of federal funding for the arts. He gripes about House majority leader Tom DeLay “jamming” his agenda down the throats of members.

What makes Houghton remarkable is that he is a Republican. But he will not be remarkable for long. One of the last of the dying breed of moderate–some would even say “liberal”–Republicans in Congress, Houghton won’t be seeking re-election this fall. After almost two decades of battling to prevent the party of Lincoln from becoming the party of DeLay, and facing the prospect of a Republican primary challenge from a conservative local official in his district, Houghton decided to call it quits. He may not be the only Republican moderate to disappear at the end of this term. Other members of what could be the most endangered species in American politics are also being hunted down by fellow Republicans as the party’s more frenzied conservatives pursue the ideological cleansing of Congress with primary challenges to New York’s Sherwood Boehlert, Maryland’s Wayne Gilchrest and other members of the House and Senate who refuse to read verbatim from the right’s playbook.

The top target this year is Pennsylvania Senator Arlen Specter, the former Warren Commission lawyer who has managed to offend both the right and left during four terms in the Senate. Specter has never been a favorite of liberals–many of whom refuse to forgive or forget his inappropriately brutal questioning of Anita Hill during the Clarence Thomas confirmation hearings. But in a closely divided Senate, Specter’s tendency to side with liberals on social issues, as well as his willingness to challenge the worst excesses of the right on judicial nominations, tax cuts, the minimum wage, school choice and tort reform, has made him a Republican that Democrats can deal with.

That’s why the radical right is pulling out all the stops to get rid of Specter, who faces an April 27 primary challenge from conservative Congressman Pat Toomey. With big-money “independent” spending on his behalf from the Club for Growth, a billionaire boys’ club that specializes in aiding primary challenges to Republicans who are insufficiently rabid, and even more essential support from the National Right to Life Committee, as well as cover stories in National Review declaring the challenge to be one of “the right fights” and cheerleading columns on the Wall Street Journal‘s editorial page, Toomey has pulled close to Specter in some polls. If they can take out a veteran senator, Club for Growth boss Stephen Moore predicts a “political earthquake” that will force Republicans from the White House on down to avoid even the slightest deviation from the right’s agenda. Some Democrats are cheering on the Toomey challenge, on the theory that a right-wing Republican should be easier for the Democratic candidate, Congressman Joe Hoeffel, to beat in November; but a Toomey-like right-winger, Rick Santorum, won Pennsylvania Senate contests in 1994 and 2000. In the realpolitik of the current Congress, the Pennsylvania AFL-CIO and key unions are pulling for Specter, as are many pro-choice and gay rights activists.

Arlen Specter is no progressive. In fact, he’s not even an Amo Houghton. But if Republicans maintain control of the Senate after November, Specter and a handful of other renegade GOPers, ranging from Rhode Island’s very nearly liberal Lincoln Chafee to conservatives with maverick streaks like Arizona’s John McCain and Ohio’s George Voinovich, could be the only roadblocks to right-wing hegemony. While it may be difficult for reasonable Americans to imagine the Republican Party pushed further right, just remember that some of the people going after Specter and other moderates this year grumbled that George Bush went “soft” when he suggested that conservatives might want to show some compassion.