Vermont Sen. Bernie Sanders went on a tweet-storm Monday calling President Donald Trump a liar who could chip away at the respect for the United States worldwide. Sanders' inspiration was the president's recent claim, made without providing evidence, that former President Barack Obama wiretapped Trump Tower in New York City ahead of the 2016 election.

Sanders quote-tweeted Trump — meaning the president's original tweet about Obama was visible — and posted "President Trump cannot continue to lie, lie, lie. It diminishes the office of the president and our standing in the world."

Sanders didn't stop there. "Trump said 3-5 million people voted illegally and that his victory 'was the biggest electoral college win since Ronald Reagan.' Both lies," Sanders added. "Trump said “it looked like a million and a half people" at his inauguration. Not even close... And Trump was lying long before he was president when he tried to delegitimize our first black president with the 'birther' conspiracy... The United States will not be respected or taken seriously around the world if [Trump] continues to shamelessly lie."

Trump has not yet responded to the Vermont senator. The former director of national intelligence, the head of the FBI and an Obama spokesman all denied the wiretap occurred. Trump made the claim Saturday morning in a series of tweets.

This isn't the first time Sanders has gone after the president on Twitter. Sanders electrified a portion of voters on the left and often finds himself starkly at odds with Trump's policies and stances.

Sanders, in fact, recently trolled Trump on Twitter about the size of his inauguration crowd, which became a perhaps odd sticking point for the president during his first few days in the White House. Sanders also spoke out against Trump after the president delivered his first major speech to a join session of Congress last week. During a video on Facebook Live, he urged folks to stay active and to continue to fight the president.

"Those of you who attended rallies or town hall meetings: Keep showing up, keep calling Congress, and continue to fight," Sanders said. "If you haven't taken action yet, we need your voice. 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 a political revolution that will turn this country around."