Gabriel Gomez, 47, gave money to President Barack Obama’s 2008 White House campaign. He supports gay marriage. Fluent in Spanish, he once worked for an investment companyfounded by President Bill Clinton’s former chief of staff, and he personally appealed to the Democratic governor of Massachusetts for an appointment to the U.S. Senate. He’s fine with some gun control and a path to citizenship for undocumented workers.

Now, Gomez is the Republican nominee for the U.S. Senate to fill the seat once held by John Kerry, who in January became Obama’s secretary of state.

Brian Camenker, who runs the Republican-leaning blog MassResistance, has called Gomez, “Another pro-gay marriage RINO” -- the dismissive acronym used by party stalwarts for Republican in Name Only.

In the same April 25 blog post, he said “Gomez is telling the media he’s ‘A New Kind of Republican.’ In other words, a Democrat.”

Gomez’s unusual dossier also looms as a challenge for opponent Ed Markey, 66, and other Massachusetts Democrats, who don’t want a repeat of 2010, when they lost a special election for a Senate seat to a fresh-faced Republican, Scott Brown.

An Emerson College poll released yesterday showed a potentially close race, with Markey leading Gomez by just six percentage points, 42 to 36 percent. Independents were flocking to Gomez, 46 percent to 25 percent, the poll showed.

Mary Anne Marsh, a Democratic strategist based in Boston, said that though the race is Markey’s to lose because of the state’s Democratic tilt, he “will have to run like his hair is on fire.”

To remind voters about the “R” next to Gomez’s name, the state’s leading Democrats held a “unity breakfast” the day after the April 30 primary and depicted him as part of the Republican machine.

“He is the candidate of the National Republican Party,” Markey said, speaking at the Omni Parker House Hotel in Boston. “He is representing the values of the National Republican Party. I think we’re in for a historically clear choice for the people of Massachusetts to make.”

The race is the first statewide contest for federal office since President Barack Obama laid out a second-term agenda that includes revising immigration policy and new gun control measures, and it’s expected to draw national attention and money. Democrats need to hold the seat to preserve their 55-to- 45 caucus advantage in the Senate.

Gomez’s primary victory win over two other candidates comes as Republicans are trying to retool the party’s image and appeal to Hispanics, who are the fastest-growing voting bloc and heavily supported Obama in the 2012 presidential race.

Obama won 71 percent of the Hispanic vote, while Republican nominee Mitt Romney, a former Massachusetts governor who said undocumented residents should “self deport,” took 27 percent - - the least for his party’s national ticket since 1996.

Gomez already is gaining attention outside Massachusetts. He was interviewed May 1 on Fox News with Greta Van Susteren. Eric Fehrnstrom, a top adviser to the Romney presidential campaign, posted a supportive note on Twitter, calling Gomez “a new breed of Republican.”

Brown, who after his 2010 Senate win was defeated last November for a full six-year term, posted on Twitter: “Congratulations to Gabriel Gomez. I look forward to calling him Senator.”

Gomez, married and the father of four, likes to tell his personal story on the campaign trail. His parents moved to Los Angeles from Colombia a year before he was born. He says Spanish was his first language.

His resume includes graduation from the U.S. Naval Academy and a stint as a Navy SEAL platoon commander deployed in the West Indies and South America. He’s also a graduate ofHarvard Business School.

After Harvard, he landed a job at an investment bank founded by Erskine Bowles, the one-time White House chief of staff to Clinton, a Democrat. He had been working for another company, the Boston-based Advent International private-equity firm, before quitting in January to seek the Senate seat.

Gomez put $600,000 toward his primary victory. In a telephone interview, he declined to say whether he would continue to tap his own resources.

“I’m highly confident I will be able to raise the money I need to compete,” he said.

Gomez said he is in line with the Republican Party on fiscal issues and wants to cut federal spending. “Even defense has room to trim,” he said. One example he cited would be to reduce by 10 percent to 15 percent the civilian employees at the Department of Defense.

Still, his positions on gay marriage and other issues could cost him support among Republican activists.

“We do have some people who would rather stay home than vote for him,” said Anne Fox, president of Massachusetts Citizens for Life, the largest and oldest anti-abortion rights group in Massachusetts. “I don’t see him giving us the assurance that he would vote properly.”

Asked in an interview what his position in Congress would be on abortion rights, Gomez said, “I’m not going there to change the law.”

Another stumbling block for other Republicans is that Gomez has opened his wallet for Democrats.

He donated $230 in 2007 to Obama’s presidential campaign, according to Federal Election Commission records. Two years later he wrote a $1,000 check to Alan Khazei, who was a candidate in the 2009 Democratic primary for U.S. Senate. Khazei lost to Martha Coakley, who then lost to Brown in the 2010 special election to fill the seat that long had been held by the lateTed Kennedy, a Democrat.

Gomez, in a letter to Massachusetts Governor Deval Patrick this January in which he sought the interim appointment to the seat Kerry vacated, stressed support for Obama initatives.

“Two main issues that will dominate the political discussion during this appointment will be immigration reform and gun control,” Gomez wrote. “I support the positions that President Obama has taken on these issues.”

That boast gives pause to some voters he will need to defeat Markey.

“We take issue with Gabriel Gomez on a couple key issues,” said Christine Morabito, president of the Greater Boston Tea Party, citing his support for gun control and immigration.

“We really need to know him better,” Morabito said, adding that “a lot of members” of the anti-tax Tea Party movement “do find the social issues really important.”

Gomez, in his letter to Patrick, also specifically noted Bowles’s link to one of his former jobs.

Democrats want to focus on another aspect of Gomez’s past. In 2012, he was a spokesman for a group called Special Operations OPSEC Education Fund, which released a 22-minute video criticizing Obama for, it asserted, politicizing the killing of Osama bin Laden in a U.S. raid.

In a news release and video issued on May 1, Markey’s campaign describes the group as a “secretly funded special interest group” that put out a “radical” video attacking Obama.

Gomez said he continues to believe the president released too much information about the 2011 raid on a compound in Pakistan where bin Laden was living

``This endangered the men and women of the United States armed services,” he said.

He added that he doesn’t plan to make that an issue in a state where Democratic voter registrations outnumber Republicans by 3-to-1.

“I’ve made my point before,” Gomez said.

To contact the reporter on this story: Annie Linskey in Boston at alinskey@bloomberg.net

To contact the editor responsible for this story: Jeanne Cummings atjcummings21@bloomberg.net