Sen. 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.) on Thursday wouldn’t rule out a 2020 presidential run, saying he wants to help rebuild the Democratic Party’s base in the wake of Donald 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’s White House win.

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“Four years is a long time from now,” Sanders told The Associated Press. "We'll take one thing at a time, but I'm not ruling out anything."

Sanders, 75, generated excitement among liberals and millennials within the Democratic Party as he challenged 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 the primaries.

In the AP interview, Sanders said Clinton’s loss was due to a “lack of enthusiasm” among Democratic voters. He also called Trump’s appeal to white working-class voters an “embarrassment” to Dems.

"It is an embarrassment, I think, to the entire of Democratic Party that millions of white working-class people decided to vote for Mr. Trump, which suggests that the Democratic message of standing up for working people no longer holds much sway among workers in this country," Sanders said.

In a Wednesday statement, Sanders signaled he’d be willing to work with Trump, but vowed he “will vigorously oppose” the Republican president-elect if “he pursues racist, sexist, xenophobic and anti-environment policies.”

The Vermont senator faces reelection in 2018 in a solidly blue state. Sanders will be 79 years old in 2020.