An AP News Analysis

WASHINGTON (AP) — Two more members of Congress have fallen to strategies that worked before, but not this year: switching parties to avoid defeat and edging to the political center in the early going.

This time it was political purists in Alabama who tossed out lawmakers from both parties in primary elections, which often are dominated by highly motivated and ideological voters.

As in Utah, Pennsylvania, Florida and other states, these voters are demanding party fealty, making the political center look slippery, at least for now. While energizing spring campaigns, their passions may cause headaches for both parties in November, when independent and moderate voters will be far more plentiful.

In Alabama, Democrat-turned-Republican Rep. Parker Griffith got clobbered in the GOP primary by Mo Brooks, who was backed by tea party activists.

Meanwhile in the Democratic gubernatorial primary, Rep. Artur Davis lost badly after running a campaign that seemed aimed mainly at the November general election. Davis, who is black, paid dearly for opposing President Barack Obama’s health care plan and for alienating important civil rights groups.

Alabama Agriculture Commissioner Ron Sparks, who is white, easily defeated Davis by running a more liberal campaign. He endorsed the health care bill and won the support of the state’s major black political groups.

Davis ran on the hope that Alabama primary voters would agree that their state will not elect a governor in November who campaigned as a mainstream national Democrat.

And Griffith, who had voted in Congress against Obama’s health bill, economic stimulus and “cap and trade” plan for carbon emissions, assumed his district’s Republican activists would embrace a conservative who switched to the GOP.

Both men underestimated the intensity of their parties’ most ideological voters, who want party purity even if it complicates matters this fall. These voters show no sympathy for politicians who appear to shift their principles, even slightly, to stay in office.

“You have a polarization happening on both the left and the right,” Washington-based GOP consultant Ron Bonjean said. For most nominees to win in November, he said, “they’re going to have to capture the center.”

For now, that seems of little concern to primary voters of either party. Earlier this year, Utah Republican convention-goers rejected conservative Sen. Bob Bennett in favor of tea party activists who are even more conservative and libertarian-leaning.

GOP activists chased mainstream Republican Gov. Charlie Crist out the Senate primary in Florida, where he’s running as an independent. In Kentucky, they chose libertarian favorite Rand Paul over a Republican establishment candidate to be their Senate nominee. In Arizona, they have forced Sen. John McCain to shift rightward to confront a hard-core conservative’s challenge.

Democratic voters have been nearly as insistent on true believers from the left.

In Pennsylvania they rejected Republican-turned-Democrat Arlen Specter’s bid for a sixth Senate term, despite Obama’s pleas. Instead they chose Rep. Joe Sestak, who campaigned in Philadelphia on Wednesday while Obama visited Pittsburgh.

Democratic voters in West Virginia rejected 14-term Rep. Alan Mollohan, although ethical problems muddied the picture there. And in Arkansas they have forced two-term Sen. Blanche Lincoln into a tough runoff primary next week after she angered union activists over health care and other issues.

The next political petri dish to fascinate campaign strategists will be Tuesday’s Republican primary in Nevada. Democratic Senate leader Harry Reid faces serious problems this fall. But some GOP consultants fear their party will blow its chances by nominating a tea party favorite whom Reid can portray as a fringe candidate.

Sharron Angle wants to abolish the federal income tax code, phase out Social Security for younger workers and turn a proposed nuclear waste dump site at Yucca Mountain into a waste-reprocessing site. Reid’s allies would prefer Angle to other possible opponents, and she seems to have momentum.

Bonjean says tea party favorites such as Paul in Kentucky, and Angle in Nevada, if she wins next week, will have to find a way to moderate their rhetoric this fall without appearing to moderate their core principles. That can be tricky for first-time candidates, as Paul learned when he publicly questioned the fairness of the 1964 Civil Rights Act.

If Alabama and Kentucky voters are trend setters, then the primary voters who soon will decide the fates of Lincoln, McCain and others will care more about ideological intensity than temperate appeals to centrists.

It’s a great sideshow and laboratory for political junkies. And it will offer fascinating and sometimes dramatic choices for voters this fall when they pick the next batch of government leaders.

EDITOR’S NOTE — Charles Babington has covered politics from Washington since 1987.