Voters from coast to coast were poised to deliver a heavy blow Tuesday to President Barack Obama's Democrats in elections likely to cost the party control of at least one chamber of Congress.

Just two years after Obama swept into office on a promise of hope and change, voters discouraged by the dismal U.S. economy were expected to hand Republicans control of the House of Representatives. Republicans were also expected to make gains in the Senate, with an outside shot at capturing the upper chamber.

In the campaign's final hours, Democrats and Republicans pressed their supporters to vote, especially in states with toss-up Senate contests, such as Pennsylvania, Nevada, Illinois, Colorado and Washington state.

"We're hoping now for a fresh start with the American people," said Republican National Committee chairman Michael Steele.

A big Republican win would derail Obama's agenda in the last two years of his term, potentially leaving Washington in political gridlock unless the president can find common ground with some of his fiercest critics. Domestic issues such as Obama's tax and spending plans would be most affected, but the repercussions would be felt internationally too, on issues such as climate change, trade and arms control.