On Tuesday, Sen. Bernie Sanders (Vt.), “the longest-serving independent in congressional history,” signed a statement affirming: “I am a member of the Democratic Party. I will run a Democrat, accept the nomination of my party, and I will serve as a Democrat if elected.” Sanders, who caucuses with the Democrats and is one of more than a dozen candidates running for the 2020 Democratic presidential nomination, has consistently run for office in Vermont as an independent.

After Sanders’ 2016 run for the Democratic presidential nomination, the Democratic National Committee decided that all future presidential candidates had to sign the pledge Sanders notarized Tuesday, obtained by NBC News. The DNC sent out the statement to all declared candidates last week, and the signed pledges were due this week.