Rep. Ted Lieu (D-Calif.) on Thursday cautioned Democrats that impeachment should only be their "last option."

"My view on impeachment is that it's like the power to declare war. It's one of the gravest responsibilities that Congress has," said Lieu, one of the 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's most outspoken critics, at The Atlantic's Recoding the Republic event in Los Angeles.

"It should never be our first option. It always has to be our last option."

Impeachment is like the power to declare war. It's one of the gravest responsibilities that Congress has. It should always be our last option says @tedlieu #AtlanticRepublic pic.twitter.com/sCP5vEf6E8 — AtlanticLIVE (@AtlanticLIVE) May 31, 2018

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But Lieu also added that he believes there is a "legitimate basis for impeachment, absolutely."

"I think it's going to depend on what the Mueller investigation reveals at its full conclusion," Lieu continued. "My personal view is ... it’s pretty clear to me the president of the U.S. has obstructed justice, at least once and probably more than once.

"I don’t think at this point in time the American people would be willing to impeach a president based on the fact that he obstructed justice. I think it would need something else ... conspiracy or complicity," he added.

A number of Democrats have pushed impeachment but the party's leadership is wary of a backlash in the 2018 midterms.

Lieu's remarks follow Sen. 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's (D-Mass.) comments on Tuesday that she is not yet ready to support impeachment proceedings against Trump.

Warren said that special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE's probe into possible ties between the Trump campaign and Russia's election interference, including whether Trump has sought to obstruct justice, should be allowed to proceed.

"I'm not there," Warren said. "Where I am is that we need this independent investigation without political interference."

"I take this very seriously. This is a serious constitutional move. My view on this is, protect the special prosecutor, let him finish his work without political interference," Warren added.

"Let him make a full report to the American people and then collectively we can make the decision about what the appropriate next step is. It's Donald Trump who doesn't want Mueller to be able to continue an independent investigation and bring it to a conclusion."