Former Massachusetts Gov. and 2012 Republican nominee Mitt Romney leads the growing pack for the GOP presidential nomination, while former Secretary of State Hillary Clinton remains far ahead among Democrats.

That’s according to a Fox News poll released Tuesday.

Click here for the poll results.

Romney dominates the field for the 2016 Republican nomination. He comes in at 19 percent among self-identified Republicans, followed by former Florida Gov. Jeb Bush at 10 percent. No other candidates garner double-digit backing.

New Jersey Gov. Chris Christie, former Arkansas Gov. Mike Huckabee and Kentucky Sen. Rand Paul each receive eight percent. Next, Wisconsin Gov. Scott Walker captures seven percent, followed by retired neurosurgeon Ben Carson and Wisconsin Rep. Paul Ryan each at six percent and Texas Sen. Ted Cruz at five percent.

Florida Sen. Marco Rubio (four percent), Ohio Gov. John Kasich (two percent), Texas Gov. Rick Perry (two percent), Louisiana Gov. Bobby Jindal (one percent) and former Penn. Sen. Rick Santorum (one percent) each receive the backing of less than five percent of Republicans.

This is the first time that Fox News has included Romney, Huckabee and Carson in its 2016 national GOP primary ballot test.

"Rumors about Romney running again are likely to get a further boost with these numbers," says Republican pollster Daron Shaw, who conducts the Fox News poll with Democratic pollster Chris Anderson.

Shaw adds, "With Romney and Bush running one and two among GOPers, you wonder if John McCain or Bob Dole want to get in on the action."

Voters who consider themselves part of the Tea Party movement are most likely to back Paul (13 percent), Cruz (12 percent), Romney (11 percent) and Carson (10 percent).

The top choices among white evangelical Christians include Romney (14 percent), Paul (10 percent), Bush (9 percent) and Carson (9 percent).

On the Democratic side, Clinton is still 50 points ahead of her nearest rival -- even though support for her is down somewhat from previous polls. Clinton receives the backing of 62 percent of self-identified Democrats. That’s down from 64 percent in July and a high of 69 percent in April.

The support Clinton has lost since April appears to be going to Massachusetts Sen. Elizabeth Warren, who captures 12 percent. That’s up from 9 percent in July -- and double the 6 percent she received in April. Vice President Joe Biden comes in close behind at 10 percent. All other possible Democratic candidates tested garner three percent or less.

"With the field of candidates still growing, the GOP primary holds potential for an extended freewheeling contest,” says Anderson, “while the Democrats continue to track toward an efficient yet boring primary season."

“At the same time,” Anderson adds, “I remember Clinton looking somewhat inevitable eight years ago too.”

Clinton led the Democratic primary pack with 33 percent to Barack Obama’s 12 percent and Al Gore’s 11 percent in a December 2006 Fox News poll.

Reminder to readers: the Iowa precinct caucuses are (some say “still,” while others say “only”) about a year away.

The new poll finds that if the 2016 general election “were held today,” Clinton would top Paul by 11 points, Christie by 12 and Kasich by 16.

Bush is the only GOP candidate tested in the hypothetical matchups to keep Clinton under 50 percent -- and to keep her advantage under double digits. She leads him by just 7 points in a head-to-head matchup (49-42 percent), which makes this the best Bush has performed against Clinton so far. Clinton was up by 13 points in March (51-38 percent).

Independents split their support, 41 percent for Clinton and 38 percent for Bush.

"One thing about Clinton that stands out is that despite a book, a world tour, numerous controversies and several distinctly different possible opponents, her support hasn't changed much over the past two years -- and doesn't depend much on who the Republican is,” adds Shaw. “Right now, Clinton is the defining feature of the 2016 race."

People think -- if they were to run -- that Clinton and Bush are more likely to be helped (41 percent) than hurt (30 percent) by being related to previous presidents. Another 16 percent say it’s a mixed bag and 2 percent volunteer that it depends on if they run against each other.

Bush announced Tuesday that he “will actively explore the possibility of running” for president.

While there’s no gender gap, Democrats (50 percent) are more likely than Republicans (37 percent) and independents (32 percent) to say the Clinton-Bush candidacies would be helped by their family connections.

What about Clinton’s role in Benghazi? Most people -- 63 percent -- say if she runs it won’t make a difference to their vote that Clinton was the head of the State Department when the U.S. consulate there was attacked and four Americans died. Among those saying it matters, by a 29-6 percent margin they say Benghazi would make them less likely to vote for her.

Almost all Democrats, fully 86 percent, say the Benghazi attacks won’t matter to their vote if Clinton runs. For independents, 55 percent say it won’t make a difference, while 36 percent say it would make them less likely to support her.

Among veterans and those currently serving in the military, 56 percent say Benghazi won’t matter, while for 40 percent it would hurt Clinton’s chances of getting their vote.

The Fox News poll is based on landline and cell phone interviews with 1,043 randomly chosen registered voters nationwide and was conducted under the joint direction of Anderson Robbins Research (D) and Shaw & Company Research (R) from December 7-9, 2014. The full poll has a margin of sampling error of plus or minus three percentage points. The results among Democrats and Republicans have an error of plus or minus five points.

Mike Huckabee is the host of “Huckabee” on Fox News Channel.”