Former vice president Biden, Senator Elizabeth Warren and Senator Bernie Sanders -- all in their seventies -- lead in national polling for the Democratic nomination.
But Buttigieg, a millennial military veteran and mayor from Indiana, has cracked into the top tier with a steady rise in the past month, particularly in early-voting states like Iowa where he has seized the momentum.
Pence aide said Trump’s Ukraine phone call was ‘unusual and inappropriate’
The 37-year-old technocrat is buoyed by an unruffled campaign demeanor and pragmatic reform proposals that have gained traction in Iowa and New Hampshire, the two states that vote first in the nomination race.
But even as the 10 qualifying candidates prepare to rumble in the fifth nationally televised Democratic debate, the showdown in Atlanta threatens to be overshadowed by impeachment hearings into President Donald Trump's dealings with Ukraine.
The first of nine current or former officials began testifying publicly this week before House investigators who grilled them on what they know about Trump's alleged coercion efforts.
Democrats accuse Trump of conditioning military aid and a White House meeting on Kiev's announcing investigations of Biden and his son Hunter, who worked with a Ukrainian energy company while his father was vice president.
Testifying just hours before the debate, Gordon Sondland, ambassador to the European Union, said he was ordered by Trump to seek a deal in which Ukraine would probe Biden in exchange for a White House meeting.
With national attention directed at Capitol Hill, the debate run-up has been low-key.
The race itself currently features 17 names after fringe candidate Wayne Messam, mayor of Miramar, Florida, pulled out.
Ten have qualified for Wednesday's debate: Biden, Warren, Sanders and Buttigieg; senators Kamala Harris, Cory Booker and Amy Klobuchar; entrepreneur Andrew Yang and investor-turned-activist Tom Steyer; and congresswoman Tulsi Gabbard.
The figure is down two from October's debate. Former congressman Beto O'Rourke dropped out, and Obama-era cabinet member Julian Castro failed to qualify this time.
The field may soon expand again to include billionaire businessman Michael Bloomberg.
The moderate former New York mayor has yet to announce he is in, but he recently filed ballot paperwork in two states, and launched a $100 million online anti-Trump advertising campaign.
Bloomberg's entry could signal lack of confidence in Biden's candidacy -- which could benefit Buttigieg, who occupies the same centrist lane.
Buttigieg is "the breakout star of this primary process," Jim Messina, the former campaign manager for president Barack Obama's successful re-election, told CNN on Monday.
Nationally, Buttigieg is in fourth position, according to a RealClearPolitics polling average.
But a new Des Moines Register poll of Iowa voters showed him storming into the lead with 25 per cent support, followed by Warren at 16 per cent and Biden and Sanders both at 15 per cent.
And a fresh, albeit small, survey of New Hampshire voters released Tuesday by St. Anselm College shows Buttigieg shooting to top spot for the first time, with 25 per cent.
That puts Buttigieg, who is openly gay, on course to face targeted attacks from debate rivals.
He has criticised Warren and Sanders for supporting a "Medicare for All" plan for universal health care that would do away with private health insurance.
Buttigieg insists his "Medicare for all who want it" proposal would kick no American off their private health plans while allowing anyone to sign up for affordable government-run coverage.
Sondland, political appointee to EU in eye of impeachment storm
With 75 days before the Iowa caucuses, significant numbers of voters say they remain undecided.
Speaking last weekend, Buttigieg said he saw a "huge opportunity" to connect with voters as he positions himself as a non-Biden alternative to liberal candidates Warren and Sanders.
Trump 2020 campaign manager Brad Parscale said he expected "another boring debate," as his team placed ads in local media touting the president's economic record and accusing the Democrats of destroying jobs.
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