Sen. Bernie Sanders Bernie SandersButtigieg stands in as Pence for Harris's debate practice Bernie Sanders warns of 'nightmare scenario' if Trump refuses election results Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (I-Vt.) announced on Monday that he’s running for reelection this year.

“Today, I am announcing my intention to run for re-election to the United States Senate in 2018,” Sanders wrote on Twitter.

I have some important news to share, and I wanted you to hear it from me: Today, I am announcing my intention to run for re-election to the United States Senate in 2018. — Bernie Sanders (@BernieSanders) May 21, 2018

Sanders, who ran for the Democratic presidential nomination in 2016, attacked 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 in a string of tweets announcing his bid and said if he is reelected, he would fight against Trump and Republicans.

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“If reelected, you can be sure that I will continue to be the fiercest opponent in the Senate to the rightwing extremism of Trump and the Republican leadership,” Sanders tweeted.

He also noted the need to fight for a progressive agenda and said he intends to run a grass-roots campaign in Vermont.

Sanders, who many see as a frontrunner for the Democratic presidential nomination in 2020, has gained a loyal following of progressives since his 2016 presidential campaign.

The senator is expected to easily reclaim his seat in the midterm elections.

He was first elected to the House of Representatives in 1990 and the Senate in 2006.