"Keep showing up. Keep calling Congress and continue the fight. The Republicans are now on the defensive and we've got to continue to push them back," Sanders said.

Sanders also made an appeal to potential skeptics of the Trump administration who have not publicly reached out to a lawmaker or attended a rally.

"Only together when millions of people stand up for economic justice, for social justice, for racial justice, for environmental justice, only then can we create the political revolution that will turn this country around," he said.

The comments echo back to Sanders's failed campaign for the Democratic presidential nomination, which he and top supporters repeatedly referred to as a "revolution."

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Democrats have voiced skepticism about Trump's message of unity during his first speech to Congress, arguing his rhetoric is out of line with the policies of his administration.

Sanders noted that Trump's rhetoric "sounds good on the surface."

"It doesn't sound so good if you dig just a little deeper beneath the service," he said, arguing Trump has broken his pledge to "drain the swamp."

He specifically pointed to Trump's rhetoric during his speech backing clean air and clean water.

"I had a difficult time not laughing out loud when he said that," he said.

Trump signed an executive order earlier Tuesday that rolled back the Environmental Protection Agency's Clean Water Rule, which expanded the federal government's oversight of local waterways.

Sanders also knocked Trump over things that he didn't mention in his speech, including the lack of a pledge to block any cuts to Medicare or Social Security.

"I did not hear President Trump say one word, not one word, about Social Security or Medicare," he said. "President Trump promised over and over and over again that he would not cut Social Security or Medicare or Medicaid."

Sanders — noting that Trump should "keep his promise" — urged the president to publicly "tell the American people [or] tweet to the American people" that he would uphold his campaign pledge.

Sanders has repeatedly called on Trump to publicly pledge to veto any cuts to Social Security, Medicare or Medicaid, including asking him earlier this month to say that to GOP lawmakers.