US President Barack Obama speaks at the University of Nevada Las Vegas on June 7, 2012 in Las Vegas, Nevada, to push US Congress to pass his proposals to create jobs and improve the economic standing of middle class families. AFP PHOTO/Jewel Samad (Photo credit should read JEWEL SAMAD/AFP/GettyImages) President Barack Obama speaks at the University of Nevada Las Vegas on June 7, 2012 in Las Vegas, Nev. (credit: JEWEL SAMAD/AFP/GettyImages)

PROVIDENCE, R.I. (CBSDC/AP) — They are trying to be hopeful, but the Democratic Party’s most passionate voters are struggling to hide their frustration with President Barack Obama.

Republicans attack the president as a big-government liberal. Many liberals meeting Thursday at Netroots Nation — it describes the annual convention as “a giant family reunion for the left” — argue instead that Obama hasn’t fought hard enough for progressive priorities on taxes, health care and the economy.

Even more problematic for the president: With the election just five months away, some are threatening not to donate money or time or even vote in November for the man who overwhelmingly ignited their passions and captured their imaginations four years ago.

“I want to be happy with him,” said Democrat Kristine Vaughan, a 45-year-old school psychologist from Canton, Ohio. “But I am finding that he has succumbed to the corporate influence as much as everyone else. I think he has so much potential to break out of that, but overall he has been a disappointment.”

RELATED: DC GOV. DOGGED BY CORRUPTION SCANDAL

Vaughan isn’t sure whether she’ll vote for Obama a second time and probably won’t donate money as she did during his first campaign. She refuses to support Republican challenger Mitt Romney, but is considering writing in another candidate in protest.

The sentiment is not unique among the 2,700 people gathered on the first day of this three-day convention. More than a dozen liberals interviewed here indicated some level of frustration with the president, despite widespread praise for his recent decision to support gay marriage and ongoing push to scale back military action in the Middle East.

Most plan on voting for Obama and their gripes are not unlike what the White House has heard for much of the president’s term. But these left-leaning backers’ varying levels of enthusiasm could spell trouble for a president whose 2008 victory was fueled by a massive network of grass-roots volunteers and small-dollar donors. Polls show the president locked in a tight race that’s likely to be decided in several swing states where he scored narrow victories four years ago. Places like Ohio, Florida and Virginia are expected to be especially competitive, and Obama will need liberal supporters to both work on his behalf and turn out in droves on Election Day.

“He’s done a good job, but he could have done a lot better,” said Ed Tracey, 55, of Lebanon, N.H., who heads his local chapter of the group, Drinking Liberally.

Tracey was one of Obama’s many small-dollar donors four years ago, but his dissatisfaction has affected his generosity: “I decided that unless I thought he really needed it, I wouldn’t contribute,” he said.

The President recently said he planned to “fight like hell” to raise more money than Romney.

Despite the criticism, polling suggests Republicans may face a larger enthusiasm gap than Democrats.

In late May, a Washington Post-ABC News poll found that 93 percent of Obama voters said they are enthusiastic about voting for him, including 51 percent who were very enthusiastic. For Romney supporters, 75 percent were enthusiastic, and just 26 percent were very enthusiastic.

Still, a closer look at the Democratic base shows an evolution of enthusiasm — or lack thereof — over the past four years.

The widespread belief in Obama’s message of hope and change turned to frustration as the president yielded to Republican pressure by devoting a significant portion of the 2009 stimulus package to tax cuts. Liberals were further irked when he abandoned the so-called “public option” in his health care overhaul, didn’t go after big banks more aggressively in his financial overhaul bill and supported the extension of Bush-era tax cuts.

Now, many say Obama is not fighting hard enough for tax increases on the wealthy to help close the federal deficit.

“I look forward to him fighting much harder,” said Arshad Hasan, executive director of Democracy for America, a group founded by former Vermont Gov. Howard Dean.

But, like many liberals here, Hasan offered a mixed review of the president. He said Obama’s decision to support gay marriage was “a huge accomplishment for progressives.” He also was hopeful that Obama might shift further to the left should he win a second term.

“There’s also a strain of thought among progressives that he’s waiting until after the election to come out and be more boldly progressive,” Hasan said. “I don’t know which way that’s going to go, but I know that either way, we get a much better deal than if Mitt Romney is elected.”

Indeed, instead of hope and change, Democrats are trying to rally around their dislike for Romney, a man whom many are still getting to know.

Massachusetts-based liberal radio host Jeff Santos held the first stop of “the Real Romney tour” at the conference. The event was designed to highlight perceived weaknesses in the former Massachusetts governor’s job-creation record and private-sector experience at Bain Capital, the Boston-based private equity firm he co-founded.

“He has no soul,” Santos said of Romney.

Romney’s association with reality television host Donald Trump drew some of the most heated criticism, especially given Romney’s unwillingness to condemn Trump’s repeated questioning of Obama’s birthplace.

“If Mitt Romney can’t stand up to a birther who’s putting out racist conspiracy theories, how can he lead on other issues?” asked Rashad Robinson, executive director of Color of Change, a liberal group that promotes African-American political influence.

Robinson said some blacks now have less enthusiasm for Obama.

“President Obama hasn’t done everything we wanted. But we know what Romney would do,” he said. “Mitt Romney has said things like he doesn’t really care about the very poor. And for a community that is facing unemployment levels the black community is facing, we may not be going to the polls with hope, but that doesn’t mean we won’t be turning out.”

(TM and Copyright 2012 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2012 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)