SAN DIEGO — Mitt Romney’s unexpected step into the 2016 presidential contest is drawing enthusiasm from the GOP’s most passionate conservatives.

But not because they want him to win. For the first time in recent memory, prominent conservatives see a Republican presidential field that could have as much competition among the party’s establishment-minded prospects — like Romney — as its fiery conservatives.

“If you have that many moderate establishment candidates, it gives an opportunity for a conservative to get in and become a serious contender,” said Amy Kremer, a national tea party activist.

Indeed, with Romney’s moves in the past week toward launching a third presidential run, three high-profile Republicans from the party’s mainstream are suddenly competing for the same group of elite donors and staffing talent, just as the crowded 2016 presidential primary season begins.

And that list — Romney, New Jersey Gov. Chris Christie and former Florida Gov. Jeb Bush — doesn’t even include a group of Midwestern governors, led by Wisconsin’s Scott Walker, who also fit the mold of accomplished, economic-minded executives driven as much by a pragmatic approach to governing as by their conservative ideology.

“We’ve never seen anything remotely like it,” said Rick Wilson, a Florida-based Republican consultant who has advised presidential campaigns. “There’s no analogous situation with three bigfoot characters in the mix.”

Kentucky Sen. Rand Paul, a likely candidate who could benefit from the competition among Bush, Christie and Romney, said during a stop in New Hampshire Wednesday: “From our perspective, the more the merrier.”

The abundance of Republican presidential prospects who put economic policy ahead of social issues comes after GOP congressional leaders succeeded last year in beating back primary challenges from farther-right, tea party-affiliated candidates on their way to reclaiming Senate control.

It also sets up a potential contest of mainstream Republicans not seen since 2000, when George W. Bush was the favorite in a crowded field, or 1988, when then-Vice President George H. W. Bush was the heavy favorite.

The unexpected competition among mainstream Republicans is welcome news for prominent social conservative Tony Perkins, president of the Family Research Council.

He said the potential establishment scrum represents a “flip” from previous Republican primaries with “multiple conservative candidates behind us that sliced and diced the vote and allowed a moderate to emerge with just a plurality.” He said the cultural conservative base has learned from that and will make “some effort to coalesce around a candidate” this time.

More than a dozen candidates are preparing for what is widely seen as a once-in-a-generation opportunity — an open White House and no Republican heir apparent with a claim to the nomination. The group features no shortage of conservatives with untested mainstream appeal, including Texas Sen. Ted Cruz, Kentucky Sen. Rand Paul and former neurosurgeon Ben Carson.

Carson joins Romney on the agenda at this week’s Republican National Committee winter meeting in San Diego, where another cultural conservative favorite, Texas Gov. Rick Perry, and Wisconsin’s Walker are also slated to appear. Other would-be presidential contenders are sending senior aides to the three-day meeting to gauge interest in a prospective run.

Romney was added to the program just 36 hours before Wednesday’s opening session, having spent the last four days phoning leading Republicans and key former supporters across the country to signal serious interest in a 2016 campaign. The development seemed unthinkable a week earlier, when Bush and Christie were seen as more than capable of satisfying the establishment’s desire for mainstream candidates with White House-worthy resumes.

“By and large, they’re all going after the same base (of donors),” said former Missouri Sen. Jim Talent, a senior adviser to Romney’s 2012 campaign and among those he called in recent days to talk about another run.

“One of the things you have to determine is whether you can raise the money, and I think that’s one of the things he’s calling around about now,” Talent said. “I would feel pretty confident about that with him. He’s always been pretty good at mobilizing support.”

Kristy Campbell, a spokeswoman for Jeb Bush, welcomed Romney to the pack this week, while suggesting the former Massachusetts governor’s efforts wouldn’t affect Bush’s plans.

Bush will not attend the San Diego gathering, but he will have volunteers on hand to engage with GOP officials.

While Bush, Romney and Christie dominated the conversation about the developing GOP race, lesser-known potential candidates are also hoping to attract attention this week.

A senior adviser to Michigan Gov. Rick Snyder, Terri Reid, is headed to San Diego to talk up her recently re-elected boss, a former CEO whose accomplishments include helping deliver Detroit from bankruptcy. Snyder is among the group of Midwestern governors, elected and re-elected in swing- or even Democratic-leaning states, who could emerge as establishment picks should Romney, Bush and Christie all flame out.

Meanwhile, Christie is indicating he may move forward sooner than expected.

He has been on a victory tour attending Republican governors’ inaugurations, which will take him to key early voting states such as South Carolina and Iowa this week, just as his team prepares to add outgoing Republican National Committee finance chairman Ray Washburne to lead its fundraising operation. Further, high-profile Republican donors in New York and Virginia are planning meet-and-greet events for Christie with donors for later this month.

Perkins said he has nothing against the early establishment favorites, noting that he supported Romney aggressively in the 2012 general election.

“But he wouldn’t be my favorite in this field,” Perkins said.