WASHINGTON - Halfway through the 2010 primary season, the fundamental tension in the American political system is becoming more clear: A liberal government is struggling to impose its agenda on an electorate increasingly responsive to an activist conservative movement operating inside the Republican Party.
Most evident in the periodic eruptions of tea party support for right-wing candidates for governor or senator, the counterrevolutionary forces have just begun to test their strength directly against the Democratic majorities that seized power from Presidient George W. Bush in 2006 and made that takeover more complete in 2008 with the election of President Barack Obama.
Saddled with the burden of attempting to enact the progressive measures on which they were originally elected and to meet the costs they inherited from two wars and the massive recession that ushered them into office, the Democrats are facing a populist backlash against the interventionist, expensive policies that Obama and others have pursued.
The struggle has dominated this session of Congress with protracted fights over health care and financial regulation that have widened the ideological gap between the parties.
The intensity and constancy of the legislative warfare have denied the public one of the main goals voters sought in electing Obama - a truce between the parties. But it is not yet clear that Republicans will be punished for declaring war on the president.
The Republicans have exploited this new emphasis on governmental austerity with significant election victories in such normally Democratic states as New Jersey and Massachusetts, and signals of potential losses for Democrats in Illinois, Delaware and Pennsylvania.
Meantime, the voters in both parties are showing the instability of past preferences by rejecting seemingly well-established incumbents in favor of untested challengers in states as diverse as Utah, Florida, Arkansas and, once again, Pennsylvania.
This has made Pennsylvania's five-term Sen. Arlen Specter the archetypal figure for this year, a man who was literally run out of the Republican Party by the challenge of a junior former House member and the ill-financed tea party movement, and then upset in his new home in the Democratic primary by an even more unknown Joe Sestak, a stranger to most voters across the state until his ads began three weeks before Election Day.
In his unwarranted euphoria after beating Specter, whose party-switching was a conspicuous example of the calculated self-interest that voters associate with professional politicians, Sestak proclaimed that his victory was "a win for the people, over the establishment, over the status quo, even over Washington, D.C."
By adding the capital to his list of losers, Sestak seemed to signal his disrespect for Obama, who had warmly endorsed Specter. And that spotlights one of the great unknowns in the unresolved tension now confronting Democratic candidates: whether to run with Obama or against him.
Republicans in Congress made their choice more than a year ago when they decided to fight Obama even on the stimulus bill that pumped billions into their own recession-crippled districts. As time has gone on and the signs of economic recovery have become clearer, Obama has shown increasing force in defending his own early action and decrying the Republican opposition.
But Democrats remain nervous about lining up behind Obama. More of them are ready to rest their hopes on the Republicans' allowing themselves to be dragged too far to the right than are signing up to promise to sustain the president in future battles to cope with the challenge of fiscal deficits.
The combination of a volatile political environment and the rapid approach of the midterm voting makes it hard for Democrats to rally behind the president. But so far, they have discovered no other strategy.
David Broder's column appears each Thursday on the Missoulian's Opinion page.