WASHINGTON — Independents who swept Barack Obama to a historic 2008 victory broke big for Republicans on Tuesday as the GOP wrested political control from Democrats in Virginia and New Jersey, a troubling sign for the president and his party heading into an important midterm election year.

Conservative Republican Bob McDonnell’s victory in the Virginia governor’s race over Democrat Creigh Deeds and moderate Republican Chris Christie’s ouster of unpopular New Jersey Gov. Jon Corzine was a double-barreled triumph for a party looking to rebuild after being booted from power in national elections in 2006 and 2008.

Elsewhere on Tuesday, Gay marriage is losing by a slim margin in a closely watched referendum in Maine.

With 417 of 608 precincts reporting, 52 percent were opposed to same-sex marriage and 48 percent were in favor.

The voters are deciding whether to repeal or affirm a state law that would allow gay couples to wed.

And Democrat Bill Owens captured a GOP-held vacant 23rd Congressional District seat in New York in a race that highlighted fissures in the Republican Party and illustrated hurdles the GOP could face in capitalizing on any voter discontent with Obama and Democrats next fall.

California Lt. Gov. John Garamendi, also a Democrat, won a special election to a vacant congressional seat, Ohio voters approved casinos and a slew of cities selected mayors, including New York, which gave Michael Bloomberg a third term.

The outcomes of Virginia and New Jersey were sure to feed discussion about the state of the electorate, the status of the diverse coalition that sent Obama to the White House and the limits of the president’s influence — on the party’s base of support and on moderate current lawmakers he needs to advance his legislative priorities.

His signature issue of health care reform was dealt a blow hours before polls closed when Senate Democratic leader Harry Reid signaled that Congress may not complete health care legislation this year, missing Obama’s deadline and pushing debate into a congressional election year. Democrats in swing-voting states and moderate-to-conservative districts may be less willing to back Obama on issues like health care after Virginia and New Jersey showed there are limits to how much he can protect his rank and file from fallout back home.

The president had personally campaigned for Deeds and Corzine, seeking to ensure that independents and base voters alike turned out even if he wasn’t on the ballot — and voters still rejected them. Thus, the losses were blots on Obama’s political standing to a certain degree and suggested potential problems ahead as he seeks to achieve his policy goals, protect Democratic majorities in Congress and expand his party’s grip on governors’ seats next fall.

Interviews with voters leaving polling stations in both states were filled with reasons for Democrats to be concerned and for Republicans to be optimistic, particularly about independents — the crown jewel of elections because they often determine outcomes.