All three are now members of the Green Party, the leftists often accused of spoiling presidential elections for the Democrats. Each of them is now running for Congress in a year when young liberal activists have energized the Democratic Party, which increasingly echoes Green Party goals on issues like health care and campaign finance. But the Greens want no part of the Democratic Party’s ascendant left wing: As much as they may loathe President Trump, they say several issues — including corporate donations and support for capitalism — have rendered both the Democrats and the Republican Party rotten to the core.

“Regular working people, families, are not being represented by the government in Washington right now,” said Mr. Cortes Barragan , a psychologist who is living with his parents while he pays off $40,000 in student loans. “That is because the Democratic Party followed the Republican Party in aligning itself with corporate America.”

A wave of liberal excitement has raised hopes for a “blue wave” in the midterms and empowered a new crop of progressive Democrats, like the democratic socialist Alexandria Ocasio-Cortez. But it has also paid dividends for the Green Party, wh ose formal endorsement of anticapitalism in 2016 helped set them apart from the Democrats and contributed to a swell of new members, many of them young people and ex-Democrats embittered by Mr. Sanders’ primary loss.

The Greens find themselves looking optimistically toward the 2020 presidential election, but it is unclear who their standard-bearer would be. Jill Stein, the party’s nominee in 2012 and 2016, said in an interview that she would like to see the party cultivate new leaders.