"He's a different candidate than he was four years ago," said Hughes, a Republican national committeewoman from Muskegon County. "There wasn't the excitement there."
Hughes and others also point to Romney's winning the straw poll at the recent Conservative Political Action Convention in Washington, which attracted thousands of the nation's most ardent conservative activists.
Yet Michigan GOP consultant Tom Shields said Santorum, now ahead of Romney in polls Romney's native state and where his father served as governor, is exciting people where Romney isn't.
Establishment Republican figures are lining up behind Romney in Michigan, including Gov. Rick Snyder. But in 2000, Gov. John Engler promised to deliver the state as George W. Bush's firewall; McCain won the primary that year.
"For whatever reason, Romney's not objectionable. But people just haven't fully warmed up to him," said Shields, who conducts public opinion polling in Michigan. "They've just refused to take the next step and marry the guy."
It foretells problems assuring the die-hard GOP activists will be lining up in November, when their phone-banking and door-knocking could make the difference in a close election against an Obama re-election campaign projected to have $1 billion to spend.
"I voted for him. I don't want to screw around because he's who we're going to end up with," said former Arizona GOP Chairman Mike Hellon, referring to his absentee primary vote for Romney. "But I talk to people who are generally reluctant to pull the trigger for him. More than anything else, that's' a problem of intensity which could be a problem in the fall."
Romney could spice things up with his running-mate choice, although some say an August announcement might be too late to lock in the GOP foot-soldiers.
"There's a lot of speculation that Marco Rubio could be the vice presidential nominee," Iowa Gov. Terry Branstad told the AP, referring to the freshman Florida senator and tea party favorite. "I think somebody like him could add some real excitement to the ticket, would be kind of a help to Romney if he does wrap up the nomination."
Candidates historically do not win close elections based on their running mate, although they have in recent elections received a temporary bump in their national poll standing. The choice can ignite passion among the party base, as did McCain's selection of Alaska Gov. Sarah Palin in 2008.
Concerns about the enthusiasm Romney generates correspond with a general dip in excitement among Republicans in a nominating campaign that has lurched one way and another in nine contests over the past six weeks.
A CNN/ORC International poll published Wednesday showed 51 percent of Republicans nationally were extremely or very enthusiastic about voting for president in the election, down from 64 percent in October.
But the dip in GOP enthusiasm, and especially Romney's three-way loss this month, is a stark warning to Romney that he cannot wait or rely on public unpopularity with Obama to provide momentum for him.
"He cannot bank on the anger against Obama among Republicans to create the turnout we need in the Fall," Florida's Bradshaw said.
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