Hillary Clinton needs to win just 17 percent of the remaining uncommitted delegates to clinch the Democratic nomination. At this point, arguments about Bernie Sanders’s platform, his movement, or his purported electability are irrelevant; he will not be the Democratic nominee for president. Sanders must know this, but he has declared he will contest Clinton’s nomination up to the party’s nominating convention in July.

It is Sanders’s prerogative to remain in the race. But exercising that prerogative makes it easier for mega-wealthy conservatives to spend hundreds of millions of dollars to lethally bludgeon both Clinton’s candidacy and the progressive agenda to which Sanders has devoted his career. This is not solely about combating the grave threat of a Donald Trump presidency. It is also about the potential of a Democratic landslide and the progressive achievements that could follow, which is an opportunity too rare and precious to squander. The best way for Sanders to advance the progressive cause is to end his campaign and unabashedly ask his supporters to join him in helping to elect Hillary Clinton.

This is about the potential of a Democratic landslide and the progressive achievements that could follow, which is an opportunity too rare and precious to squander.

Sanders has earned the support of millions of Democrats, and the respect of even many ardent Clinton supporters. He has drawn attention to inequality, and to the economic and political influence of Wall Street. He has broadened the political debate and expanded the Democratic Party’s horizons. None of this will change if he steps aside now. On the flip side, what would Sanders gain by dragging out the nomination? Many Democrats are eager to wrap up the intra-party debate and take the fight to Trump. He’s in an optimal position to win concessions from Democrats, and will lose leverage as the nomination drags on.

Sanders supporters, resisting calls for him to end his campaign, point out Clinton did not end her 2008 campaign against Barack Obama until June. For what it’s worth, Clinton should not have stayed in the race that long. But the Clinton campaign did at least have a rationale for hanging around. Michigan and Florida had flouted the Democratic National Committee’s nominating schedule, and their delegates were not allocated until the DNC rules committee met in the last week of May. Had Clinton won a more favorable distribution of those delegates, she would have been within 100 pledged delegates of Obama, giving her hope for a miracle at the convention. Instead, a week after the DNC’s meeting, she ended her campaign. Sanders has no potential delegate windfalls awaiting him. The trajectory of the race is set, and Clinton will win on the first ballot.

Sanders supporters also claim that the extended nomination fight in 2008 laid the foundation for Obama’s massive field efforts that fall. That may have been true in some states in 2008, but none of the states remaining this year will be competitive in a close race. Besides, Sanders is not spending his money on field organizing, but on television ads in safely Democratic California. Sanders’s campaign can no longer be seen as an investment toward a Clinton victory in November.