Sen. Bernie Sanders took aim President Trump Monday morning during an appearance at Labor Day union breakfast in the state that holds the first presidential primary, but kept mum on a possible second White House bid for himself.

The longtime independent senator from Vermont - who energized progressives across the country as he battled eventual Democratic presidential nominee Hillary Clinton in the 2016 campaign - sparked more speculation about his 2020 presidential ambitions as he headlined the New Hampshire AFL-CIO's annual Labor Day breakfast.

In his speech, Sanders blasted Trump, saying: "We have a president, and I say this with no joy in my heart, who is a pathological liar."

Sanders added: "We have a president for cheap political reasons who is trying to divide us up."

Sanders claimed that Trump has been teaching people to "hate other people because they may have been born in a different country, color of their skin is different, their religion is different, their sexual orientation may be different."

Sanders also repeatedly charged that the Republican majority in the Senate and House "are exactly on the wrong side of where the American people are."

The Vermont lawmaker, who headlined the New Hampshire Labor Day breakfast for the fifth straight year, urged voters to stand together.

"We need to stand together and we will not allow Trump or anybody else to divide us up based on color of our skin, our religion, our nationality, or our sexual orientation," he said. "When we stand together we win. When they divide us up, they win."

Sanders, who is running for re-election in Vermont this November for a third term in the Senate, didn't make any references to the next White House race. Instead, he highlighted his progressive agenda, including his signature platforms of Medicare for all and a $15-per-hour minimum wage.

"I was in New Hampshire three years ago, coming before you and the people of this state, and I said, we need to move toward a Medicare-for-all single-payer program," Sanders said. "Seemed like a radical idea then. Oh my god, single payer, Medicare for all, radical idea."

He added: "I'm proud to tell you that legislation that I've offered in the Senate raising the minimum wage to $15 per hour now has 30 co-sponsors, and all across this country, cities and states are moving towards $15 an hour."

The senator also pushed for strengthening Social Security, income equality and new gun laws during his speech.

"We come from rural states, New Hampshire and Vermont," he said. "And a lot of our people hunt and own guns. But I believe that in our states and throughout this country, the overwhelming majority of the American people support common-sense gun safety legislation."

Sanders crushed Clinton in the 2016 New Hampshire primary, launching him into a months-long fight with Clinton for the Democratic nomination. Many of his top supporters from that campaign were in the audience at the Labor Day breakfast.

"I think Bernie's message is spot on - we need to come together and we'll figure out the way to do that with whomever is leading the charge,” said Executive Councilor Andru Volinsky, who was legal counsel and a member of the steering committee for Sanders' campaign in New Hampshire. "It will take a little bit to work out, but I think we're going to be fine."

Asked if the New Hampshire voters were ready for the possibility of another White House bid by Sanders, Volinsky said, "I think we have quite a crew. And that crew is still here and I see them at these events all the time."

Sanders' son, Levi, a New Hampshire resident, is one of 11 Democrats currently running for the open congressional seat in the state's 1st District. However, the elder Sanders has stayed neutral in the race and has refrained from endorsing his son since Levi Sanders announced his candidacy in late February.

Still, the senator did give his son a very quick shout-out near the beginning of the speech, saying, "Let me also thank my son Levi, who is here. Levi, stand up."