With greater success the Vermont senator now faces greater challenges. Sanders is enduring intensified criticism from Clinton and sharper scrutiny from the news media, especially after a stumbling interview with the New York Daily News editorial board in which he could not entirely explain how he would implement some of his core ideas. And for all his recent victories, Sanders’s team understands he can’t overtake Clinton just by taking predominantly white states like Wisconsin; he still must prove he can appeal to the diversity of the Democratic coalition. “We have to do that,” said Tad Devine, Sanders’s senior strategist. “I get it”

But none of that obscures what Sanders has already achieved, and how it may change the Democratic Party. At my request, the veteran electoral analyst Rhodes Cook, publisher of an eponymous political newsletter, compiled figures comparing Sanders’s performance with previous outsider challengers. Those numbers show that Sanders is on track to win more total votes, and a higher percentage of the primary vote, than any insurgent Democrat in the modern primary era.

Through Wisconsin, Cook calculates, Sanders has won about 6.65 million votes across 21 primaries, some 41 percent of all ballots cast. That means Sanders has captured a greater percentage of the total primary vote than such previous insurgents as Howard Dean in 2004 (6 percent), George McGovern in 1972 (25 percent), Jackson in 1988 (29 percent), Gary Hart in 1984 (36 percent), and Ted Kennedy in 1980 (37 percent). In actual primary votes, Sanders has already soared past Dean, McGovern, and Hart and is guaranteed to top Jackson (almost 6.7 million) and Kennedy (just under 7 million) after the April 19 New York primary alone. Measured by the share of available delegates he’s won (nearly two-fifths, including super delegates), Sanders also seems likely to outshine all these predecessors except McGovern, who captured a majority and the nomination. Only President Obama, in his 2008 primary victory, outperformed Sanders on all those fronts, and as a former keynoter at the national party convention who drew support from key party leaders, Obama doesn’t seem perfectly analogous.

These gains reflect Sanders’s advance from the beachhead on which he began the race. He started as the classic “wine track” candidate relying primarily on young people and white-collar “Volvo liberals.” But he’s competed with growing effectiveness for blue-collar whites, especially across the Midwest, which has allowed him to battle the front-runner to a draw among white voters overall. While Clinton has won among all white voters in nine of 10 Southern states with exit polls, he’s carried most whites in nine of 11 states outside the South. Sanders also has captured 10 of 13 caucuses.

Clinton’s lead rests upon her edge among Hispanics and especially African Americans, who have provided her over three-fourths of their votes and keyed her victories across most big states. Sanders must dramatically change that equation if he has any chance, as his campaign hopes, of convincing super delegates to abandon Clinton by beating her on the campaign’s final day in both New Jersey and California—two states where whites will likely comprise only about three-fifths or less of voters. “It is going to come down to California and New Jersey,” says Devine. “If we are to win this thing...we are going to have to win big at the end.”