WASHINGTON — Former Texas congressman Beto O'Rourke is sitting in third place in the Democratic presidential field, behind only former Vice President Joe Biden and Sen. Bernie Sanders, the runner-up for the 2016 nomination, according to a national poll released early Thursday.

The Quinnipiac University Poll shows Biden with 29 percent support among Democrats nationwide, a commanding lead, though some strategists suspect that will slip if and when he jumps into the race.

Sanders is at 19 percent and O'Rourke is at 12 percent.

The three Bs — Biden, Bernie and Beto — sat atop the polls in December as well, three white men in the most diverse field of contenders in history, representing a huge range of experience and ideology.

California Sen. Kamala Harris is the top choice of 8 percent of Democratic voters in the new poll, putting her in fourth place.

No other contender topped 4 percent. Julián Castro, the former San Antonio mayor and housing secretary in President Barack Obama's second term, registered 1 percent.

Historically, the eventual nominee in either party is almost always in the top three by this point in a primary fight. That's been true in seven of the last nine primaries without an incumbent. Since 1996, Donald Trump is the only nominee in either party who wasn't even in the top five in polls taken between the midterm elections and the following January.

O'Rourke, an El Paso Democrat, launched his campaign two weeks ago in Iowa and plans a more formal and extravagant rollout Saturday with rallies in his hometown, Austin and Houston, plus more than 1,000 watch parties across the country.

National polls reflect relative momentum and buzz that often drive media attention and donations, though, of course, parties don't pick their nominees in a nationwide contest.

It's a state-by-state slog, starting in Iowa on Feb. 3. New Hampshire holds its primary eight days later, followed by Nevada and South Carolina as the only other contests in February. The field of battle explodes on March 3, a Super Tuesday with simultaneous contests in Texas and California and nine other states.

An Iowa poll from Emerson College released Sunday showed that O'Rourke has just 5 percent support, well behind Biden (25 percent), Sanders (24 percent) and Pete Buttigieg, the mayor of South Bend, Ind.

O'Rourke raised a record $6.1 million in the first 24 hours after announcing his campaign, edging past Sanders, who also had an eye-popping first-day haul. Both have proven masterful at drumming up vast numbers of relatively small donations.

Biden has consistently topped polls of Democrats eyeing the White House in 2020, with Sanders consistently in second place. O'Rourke was third in late 2018 but began to slip in January and February as other candidates entered the race and he remained undecided.

Sanders and Harris each surged in polls after launching their campaigns, though Harris' spike faded fast. O'Rourke got little bounce, but may yet after this weekend's rallies in Texas.

All of the active campaigns have been pleading for donations, filling supporters' inboxes with emails ahead of an end-of-month deadline for campaign finance reports due in mid-April.

The totals will be watched closely as a gauge of staying power.

A Quinnipiac survey in December that focused on favorability ratings showed Biden especially well-positioned, with the best ratio of favorable to unfavorable ratings of any potential Democratic contender — 53-33 percent.

Sanders' rating was about split, 44-42. O'Rourke, less well-known nationally, scored 24 percent favorable, 20 percent unfavorable.

Biden, with nearly three decades in the Senate and eight as vice president under Obama, clearly has the most relevant experience. Sanders built an insurgent movement in 2016, though many of his loyalists have drifted away, shifting their gaze toward O'Rourke, Sen. Elizabeth Warren and others.

Anecdotally, many activists who backed Sanders in 2016 say they'd prefer someone younger this time around.

Biden is 76. Sanders is 77. O'Rourke is 46, and while he has never mentioned his rivals' ages, he has underscored his youthfulness by climbing on a car in Nevada and on coffeehouse countertops in Iowa to address crowds.

But Quinnipiac found that 70 percent of Democratic voters say age is not important. Far bigger factors cited include political ideology (72 percent) and the perception that someone can win (76 percent).

Nearly as many Democrats say they want bipartisanship (67 percent) as those who want someone who'll stand up to Republicans (71 percent) — a tension that poses a messaging challenge for candidates.

Although this year's field has the most women and nonwhite candidates of any in history, Democrats say overwhelmingly that race and gender is not important.

"Hungry for a candidate to take on President Donald Trump, Democrats and Democratic leaners put the three B's, Biden, Bernie and Beto, at the top in a race where age, race and gender take a back seat to electability and shared views," said Tim Malloy, assistant director of the Quinnipiac University Poll.

The poll surveyed 1,358 voters nationwide from March 21 to 25 — that is, starting one week after O'Rourke launched his campaign. Of those, 559 were identified as Democrats or voters who lean Democratic. For that subset, the margin of error is plus or minus 5.1 percentage points, meaning that each finding could vary by that much in either direction.