BOSTON: Dogged optimism rapidly gave way to somber resignation among supporters at Mitt Romney's election watch event Tuesday as it became clear that his long campaign was heading for a dead end.

The Republicans who had gathered for what they hoped would be a raucous victory party held out hope for a few tenuous hours, even as the seesaw battle tilted against them, with President Barack Obama winning state after state.

As the election unfolded on news networks shown on large video screens, a nervous quiet settled over the thousand or so Romney supporters in a large convention center ballroom in the campaign's headquarters city of Boston.

“We've gone from anxious and excited to anxious and kind of worried,” said real-estate broker Jackine Morein, 36, as she fidgeted with a half-filled plastic wine glass.

“It is quiet. I expected it to be a little more active,” she said.

But then at 11:14 pm (0314 GMT Wednesday), as many stared at the large video screens set up on either side of a “Believe in America” digital banner, the bottom fell out: Fox News called the state of Ohio for Obama.

The Romney supporters turned statue-still. Eyes grew moist, and a few couples hugged. Men in suits stared into their drinks. Friends rubbed each others backs in consolation.

“I just can't believe our country would want to go through four more years of this,” said distraught homemaker Suzanne Beck.

“I'm totally shocked,” the 50-year-old said after composing herself.

Brad Marston, a Republican strategist from Massachusetts and partner at FourTier Strategies, used some sharper language to describe the political devastation wrought in a few brief hours, including the Democrats maintaining control of the US Senate.

“We got our ass kicked tonight,” he told AFP.

It began with Massachusetts. A Romney victory in the Democratic-leaning state where he served as governor was highly unlikely, but when Fox News called the state for Obama at about 8:00 pm (0100 GMT), the room turned somber.

A Romney son, Craig, was brought in to try and liven up the crowd, but it was miserably insufficient.

“What a night. What a night,” he told the few hundred people gathered in the ballroom at the time. Many appeared unsure of what he meant.

The press risers in the room were abuzz with the nation's top media outlets, but while the reporters broadcast live from the room, the backdrop more often than not was sedate.

Pennsylvania's Republican Governor Tom Corbett conducted a quick video phone-in to the crowd to try and generate some energy, stressing the “distinct possibility, and hopefully a probability...of winning Pennsylvania.”

It didn't happen. US networks called the state for Obama.

“No, no, nooo, Pennsylvania!” one woman said under her breath.

But when Wisconsin – home of Romney's running mate Paul Ryan – and New Hampshire fell into Obama's corner, the gasps and groans were painfully audible.

“There are just a lot more have-to-win states” than at the beginning of the evening, Karen Wickers, a stay-at-home mother from California, told AFP.

Wickers said she and others in the room were closely watching Florida and Virginia, and of course the ultimate battleground of Ohio.

Florida had her worried. “It's closer than we were expecting,” she said, the creases clear on her forehead as she stared up at the screens showing the Sunshine State at 50 per cent apiece for Obama and Romney.

“Virginia, we have to win Virginia,” she pleaded.

A victory for Romney in North Carolina, a red-leaning state that had been considered a toss-up by some, woke up the crowd at about 11:00 pm, but then came California for Obama moments later.

Its 55 electoral votes pushed Obama's secured tally to 244, just 26 short of the 270 electoral votes needed for victory.

And then there was Ohio.

Conversation in the room ground to a halt, and people stared blankly at the screens. With a few other small states going quickly for Obama, it was over.

Some people quietly filed out of the room.

But then a loud cheer rose up as Fox announced that the Romney campaign was contesting the networks' Ohio call for Obama.

Minutes later, when screens showed CNN broadcasting live from the Romney room, with anchor Candy Crowley describing the mood there, the crowd began booing loudly, until organizers changed the channel.

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