NEW YORK — Bernie Sanders signaled a formal endorsement of Hillary Clinton is imminent, saying that Republican Donald Trump is “a pathological liar” and that he'll throw his full support behind electing his rival for the Democratic nomination as president.

“We have got to do everything that we can to defeat Donald Trump and elect Hillary Clinton,” the Vermont senator said in an interview Thursday with Bloomberg's Albert Hunt for PBS' “Charlie Rose” program. “I don't honestly know how we would survive four years of a Donald Trump” as president.

The endorsement, which may come as soon as next week, would provide a long-awaited unity moment for party members frustrated by Sanders' lingering campaign. Sanders has spent the weeks since Clinton clinched the nomination in early June working to influence the party's governing agenda.

Sanders expressed satisfaction with the progress of policy and party platform talks between his campaign and Clinton's, even as some positions on issues such as trade and fracking remain unresolved. “At the end of the day, we're going to be united,” he said.

Clinton announced Thursday she would campaign Tuesday in New Hampshire, the same state where she gave her endorsement to then-Sen. Barack Obama in 2008.

Sanders declined to say whether he could embrace Sen. Tim Kaine of Virginia, whom many Sanders supporters see as too accommodating of Wall Street, if Clinton taps Kaine as her running mate.

“I know Tim; Tim is a very decent guy,” Sanders said.

“I happen to believe that we should have as our vice presidential nominee a very strong, progressive voice, somebody who has a history of standing up to big money interests, somebody who is gonna fight for the working families of this country and who has a history of doing that,” Sanders said.

Sanders didn't hesitate when asked if another potential Clinton running mate, Massachusetts Sen. Elizabeth Warren, meets the test.

“I would be pleased” if Clinton chooses Warren, Sanders said, calling her “one of the outstanding members of the United States Senate.”

Asked whether FBI Director James Comey's critique of Clinton's email practices could have made a difference in the outcome of the Democratic primary, Sanders said, simply, “I have no idea.”

He said he disagrees with calls by House Speaker Paul Ryan of Wisconsin and other Republicans to deny intelligence briefings to Clinton, as are customary for presidential nominees, in light of concerns about her use of a private email server while she was secretary of state.

Sanders said Clinton's email practices remain a “relevant issue” for voters as do questions about Trump's business background and practices. At the same time, he said, both are less important than the shrinking of the middle class in the U.S., and he criticized the media's focus on superficial issues that he said took time and attention away from the country's biggest challenges.

In a show of respect for Sanders, Clinton this week embraced a plan to make in-state, public college tuition free for families earning up to $125,000 per year, moving her closer to Sanders' call for free college tuition for all Americans.

A draft of the party's platform that will be presented to delegates at the Democratic convention later this month also reflects the influence of Sanders by taking a leftward turn from 2012 on a range of issues, from regulation and taxes to support for a $15 minimum wage.

Sanders called it “the most progressive platform in the history of the Democratic Party.”