After early triumphs in the Democratic primary, the independent from Vermont failed to pull away from former Vice President Joe Biden as a wide field dwindled. Sanders saw success from Iowa to New Hampshire, Nevada, Colorado and California.

But he fell behind in the national delegate race as prominent Democrats, worried that he could become their nominee and face President Donald Trump in November, coalesced around Biden. After a string of primaries in mid-March, the former vice president racked up pledged delegates and became the race’s clear front-runner.

Sanders ran on the promise of a political “revolution” and touted his signature single-payer “Medicare for All” plan on the campaign trail. He also promised to cancel student debt and pass free universal child care — popular proposals to expand the social safety net that his rivals nonetheless criticized as unrealistic and expensive.

The senator lapped the field in fundraising with perhaps the most successful small-dollar fundraising operation ever. Though Sanders saw sustained success among young and Latino voters, Biden consistently won over black voters and older Democrats as he topped Sanders in a series of key states such as Texas.

Biden also won Michigan. Sanders had pulled off a stunning upset over eventual Democratic nominee Hillary Clinton there during the 2016 primary campaign after trailing her by double digits in polls.

A week after his Michigan triumph, Biden crushed Sanders in Florida, another delegate-heavy state.

As centrist candidates dropped out of the race to endorse Biden before and after Super Tuesday on March 3, Sanders decried an effort by the party establishment to defeat him.

Sanders’ period as the race’s front-runner followed a remarkable rebound from a heart attack last year. The oldest candidate on the campaign trail, Sanders experienced “chest discomfort,” during an Oct. 1 event, according to campaign advisor Jeff Weaver.

Testing revealed a “blockage in one artery” and two stents were inserted, Weaver added. He missed only a small amount of time on the campaign trail.

Sanders first vaulted to national fame with a strong 2016 primary race against Clinton.

This story is developing. Please check back for updates.