The midterm elections have shaken up the early race for the 2020 Democratic presidential nomination.

Enthusiasm for a White House bid by Rep. Beto O’Rourke is soaring after he came within 3 percentage points of Sen. Ted Cruz Rafael (Ted) Edward CruzTrump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy MORE in the Texas Senate race.

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O’Rourke, seen as more of a dark-horse candidate in 2020 just a few weeks ago, is suddenly being embraced by former aides to President Obama, who are comparing him to their former boss. And he’s not ruling out a White House run after dismissing it as a Senate candidate.

The Texan isn’t not the only potential candidate with new momentum after the midterms, either.

Sen. Sherrod Brown Sherrod Campbell BrownSenate Democrats release report alleging Trump admin undermined fair housing policies Bipartisan praise pours in after Ginsburg's death Emboldened Democrats haggle over 2021 agenda MORE, fresh off a decisive reelection victory in Ohio, is openly considering a run for the White House.

Democrats are giving him a fresh look, too, given his win in a perpetual swing state where President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE handily defeated Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE in 2016.

Democrats focused on winning back working-class voters are wondering if Brown’s brand of populism and socially liberal politics would make him a credible national candidate.

“Beto’s campaign has certainly catapulted him into the conversation,” said Adam Hodge, a Democratic strategist and former Democratic National Committee official. Likewise, he added, “Brown is getting a first look. Like Beto, he ran an authentic campaign that spoke directly to voters and did it in a battleground states that Democrats shouldn’t give up.”

The new momentum for O’Rourke and Brown will create fresh challenges for other would-be contenders who have long been seen as likely 2020 Democratic candidates.

The field of challengers to Trump is expected to be large, and Democrats will be looking for lanes to distinguish themselves in the crowded contest.

That includes former Vice President Joe Biden Joe BidenOmar fires back at Trump over rally remarks: 'This is my country' Trump mocks Biden appearance, mask use ahead of first debate Trump attacks Omar for criticizing US: 'How did you do where you came from?' MORE and Sens. Bernie Sanders Bernie SandersButtigieg stands in as Pence for Harris's debate practice Bernie Sanders warns of 'nightmare scenario' if Trump refuses election results Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (I-Vt.) and Elizabeth Warren Elizabeth WarrenHarris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda Judd Gregg: The Kamala threat — the Californiaization of America GOP set to release controversial Biden report MORE (D-Mass.), who have long been seen as top contenders in part because of their name recognition.

“The race has kind of flipped on its head in a really short time,” said one Democratic donor. “All of a sudden, it looks like the front-runners aren’t really the front-runners anymore.”

Democrats have long seen Biden as a strong general election candidate but have questioned his ability to win a primary against more liberal Democrats.

He would face real competition from Brown, who is to Biden’s left on trade, but also from Sen. Bob Casey Robert (Bob) Patrick CaseySecond GOP senator to quarantine after exposure to coronavirus GAO report finds brokers offered false info on coverage for pre-existing conditions Catholic group launches .7M campaign against Biden targeting swing-state voters MORE (D-Pa.), who like the senator from Ohio won reelection convincingly in a state won by Trump in 2016.

Biden, who hails from Scranton, Pa., has long been considered a candidate who could appeal to blue-collar white voters. But that is also the demographic that Brown or Casey could shoot for.

The former vice president might also have to compete with O’Rourke for the Obama crowd, judging from the effusive remarks about the Texan made by the ex-president’s former aides.

Former New York City Mayor Michael Bloomberg is also seriously considering a White House bid as a Democrat, fresh off an election cycle in which he poured cash into races to help Democrats win back the House.

Bloomberg, who would run as a centrist, could be a threat to Biden in that lane of a primary.

O’Rourke and Brown could also suck up the oxygen that other candidates need, including Sens. Kamala Harris Kamala HarrisButtigieg stands in as Pence for Harris's debate practice First presidential debate to cover coronavirus, Supreme Court Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (D-Calif.), Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (N.J.) and Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (N.Y.).

Strategists say candidates will have to figure out how quickly to launch campaigns to try to get attention from donors and the public.

They say established candidates might want to jump in quickly to blunt the momentum of a Brown or O’Rourke, for fear they could rev up like Obama’s campaign in 2008.

“[The Clinton campaign] gave him an opening and he ran through it,” said Democratic strategist Chris Kofinis. “If I’m more of an established kind of candidate, if I’m a Biden or a Warren, you can’t wait. You’ve got to be out there really fast with a strong message.

“The advantage someone like Beto has is that he has nothing to lose,” Kofinis added. “That is a dangerous candidate in a multi-candidate field. Same as Obama. Look at the kind of campaign he ran. He had nothing to lose.”

There are signs that some of the politicians long seen as 2020 candidates are getting into the deeper water.

Warren this week rolled out a foreign policy vision focused on free trade agreements. Speaking at American University, she said foreign policy should “benefit all Americans, not just wealthy elites.”

Other candidates are on the move to early primary states. Booker is heading back to New Hampshire to headline a “post-election victory celebration,” the state party announced on Friday.

Harris crisscrossed Iowa last month and proposed a tax credit of up to $500 a month for families earning less than $100,000.

Every day, the potential field grows seemingly larger.

Last week, former Secretary of State John Kerry John Forbes KerryThe Memo: Warning signs flash for Trump on debates Divided country, divided church TV ads favored Biden 2-1 in past month MORE, the Democratic nominee in 2004, said he was mulling a run in 2020.

“Everyone is deciding they have an opening based on their own facts,” said Kofinis.

The elbows may begin to fly.

Chicago Mayor Rahm Emanuel (D) on Thursday said it would be unusual for the party to nominate O’Rourke in 2020 since you usually don’t nominate losers — a pointed reference to the loss to Cruz.