Washington ? People say they don’t like partisan gridlock in Washington. But they’re voting in ways almost certain to increase it, by punishing politicians who cooperate with the opposing party and rewarding ideological purity that pushes both sides to the fringes.

In the past few weeks, Democratic voters have ousted one of Congress’ best-known centrists, Sen. Arlen Specter of Pennsylvania, and forced another, Sen. Blanche Lincoln of Arkansas, into a difficult primary runoff June 8.

Republican activists ended the career of conservative three-term Sen. Bob Bennett of Utah in part because he had worked with a Democrat on a health care bill, which went nowhere. In Arizona, they have sent a once-famous maverick, Sen. John McCain, scurrying to the right to save his political skin.

Aside from good political theater, these dynamics profoundly affect government policy. Efforts to revamp energy, immigration and other big policies have flagged largely because of partisan divisions, especially in the Senate, where filibuster rules allow a united minority party to stop all but a few bills.

Even before these recent primaries, Congress was pushing the limits of partisanship. This year’s landmark health care law passed without a single Republican vote. President Barack Obama’s visit last Tuesday with Republican senators dissolved into testy exchanges, no thaw in hostilities apparent.

Indeed, to many political activists, merely talking with the other party is unforgivable.

South Carolina’s Charles-ton County Republican Party condemned Sen. Lindsey Graham, R-S.C., last year for undermining “Republican leadership and party solidarity” by working with Democrats on an energy bill that remains stalled.

The American Conservative Union gives Graham a lifetime score of 89.68 percent, a fraction higher than those of GOP stalwarts Orrin Hatch of Utah and Mitch McConnell of Kentucky, the Senate’s Republican leader.

In upstate New York, conservative activists were so incensed by a Republican House nominee’s centrist views that they backed a tea party candidate and handed a special election to an underdog Democrat. Tea party leaders said the sacrifice was worthwhile.

Voters who want bipartisanship are mostly in the political middle, said Nebraska Democrat Ben Nelson, one of the Senate’s most centrist members. Activists on the left and right often dominate the nomination process, and demand ideological loyalty, he said.

“You squeeze the middle out, and then there will be more criticism of the lack of bipartisanship” without an awareness of “why there is less bipartisanship,” Nelson said. He noted that a liberal group ran ads attacking him last year when he refused to support a government-run health insurance option.