When a GOP filibuster left McCain-Feingold stuck in a ditch last fall, Senate Democrats came up with a cunning plan to get it moving again — tie the promise of a straight up-or-down vote on campaign finance reform to the utterly unrelated highway bill. No senator in his or her right mind, they reckoned, would hold billions in road, bridge and mass transit pork hostage to a silly little issue like good government.

They reckoned right. Republican leadership caved and scheduled a simple-majority vote on McCain-Feingold by March 6, grousing all the way about this egregious abuse of lawmaking procedure.

Well, the grousing’s over and the tables have been turned. The highway bill now will be tied to the Republican’s favorite unrelated pet project — the death of affirmative action.

The first skirmish will be over a program that steers at least 10 percent of transportation funds to minority and women-owned construction businesses. Sen. Mitch McConnell of Kentucky, who hates affirmative action almost as much as he hates campaign finance reform, plans to attach an amendment to kill the minority set-aside program. While that at least has something to do with highways, it has little to do with the return to the states of the billions they send to Washington in fuel taxes.

After that, it’s unrelated all the way. Other baggage that may end up stuffed in the trunk of the highway bill includes scores of programs to boost women and minorities, the appointment of Bill Lann Lee to the Justice Department’s top civil rights post, legislation to outlaw job discrimination against gays and President Clinton’s proposal to increase funding for civil rights enforcement.

The Democrats, of course, asked for it. They put Republicans in the uncomfortable position of having to choose between peddling influence and fixing potholes. Now they have to choose between fixing potholes and keeping programs of vital importance to their core constituency. They never saw it coming.

Campaign finance reform is good. A thoughtful scrutiny of affirmative action programs — that is, the use of taxpayers’ money to level the playing field — would be a good. Hooking either of these issues up to the highway bill’s trailer hitch is not good, but it is business as usual.

Members of Congress routinely fuss and fume about this unrelated amendment scam, about how deceptive and devious it is, about how it must be stopped. In fact, if the the American taxpayers had a dollar for every time that heard that whine, they wouldn’t need the highway bill at all.