WASHINGTON -- A year after Barack Obama's election stirred broad hopes for change among American voters, persistent high unemployment and the spectacle of continued gridlock in Washington threaten Democratic dominance of the political landscape.

Tuesday's defeats in gubernatorial elections in Virginia and New Jersey not only ended a decade or more of Democratic gains in those states but signaled possible trouble ahead in the midterm elections at the national level.

At the same time, the loss of another Republican House seat in a special election -- the fourth such defeat in the last two years -- showed how bitter ideological conflict within the party could cripple the GOP's prospects for a comeback.

Despite White House efforts to discount the importance of the loss of the only two governorships on the off-year ballot, especially in New Jersey, where Obama had campaigned heavily for embattled Gov. Jon Corzine, the implications were clear to other Democrats.

Rep. Jim Cooper of Tennessee, a leader of the moderate-conservative "Blue Dogs," called the result "a wake-up call for Congress. A tidal wave could be coming."

His fellow Tennessean, Republican Sen. Lamar Alexander, said that Obama "retains his personal popularity, but his policies, and those pushed by the congressional Democrats, are scaring the daylights out of people."

Democratic pollster Peter Hart, in a memo to his clients, warned of the possible consequences of "the disappointment and disgust the American public feels toward Washington. It is as strongly negative as the period of 1979-80 and 1973-74." Both those cycles saw wholesale changes in Congress, the Democrats benefiting in the latter and the Republicans in the former.

For Obama and the Democratic congressional leadership, the off-year results arrived at a moment when their fragile internal coalitions are facing severe tests. The White House is attempting to stage-manage a crucial vote-counting exercise in both the House and Senate to determine if Democrats can risk bringing landmark health care bills to the floor. And within weeks, Obama may precipitate a similar test of support on a new policy toward Afghanistan.

Former Republican Rep. Vin Weber said he sees the Democrats in "a difficult position. A year ago, they thought they were entering a new progressive era. It was 1932 again. But within a couple months, it began to turn around, and worries about spending and big government came to the fore. In New Jersey and Virginia, we're seeing the voters return to a center-right agenda. But I think Obama and the Democratic congressional leaders are locked into that progressive agenda, and that leaves them in a risky position."

Weber conceded that "the grass-roots energy" fueling signs of a Republican comeback "can be destructive" when it is less well managed than it was in the two successful gubernatorial campaigns. In both New Jersey and Virginia, candidates with clear conservative histories and credentials, former prosecutors Chris Christie and Bob McDonnell, focused their races on their opposition to higher taxes and their proposals for attracting jobs.

On the other hand, the GOP civil war that broke loose in New York's 23rd District special election resulted in the loss of a seat that had been Republican for more than a century. Democrats said they looked forward to many more instances next year where conservative icons such as Sarah Palin and Glenn Beck intervene against mainstream Republicans.

While that problem concerns Republicans, Democrats have a larger worry: the unemployment crisis that crippled John McCain and the Republicans in 2008 is hanging on -- and now is being blamed on Democrats.

Exit polls in New Jersey and Virginia showed that the more worried voters were about keeping or finding a job, the more likely they were to vote Republican.

Last week, I heard the lead economist for a major New York bank predict that unemployment next November will still linger at 9.5 percent or more.

If that is the case, this week's Democratic losses could seem minor by comparison.

David Broder's e-mail address is davidbroder@washpost.com.