Hillary Clinton may have amassed a nearly insurmountable lead in delegates, but rank-and-file Democrats are now virtually split between her and Bernie Sanders over which candidate should be their party’s presidential nominee, according to a new PRRI / The Atlantic poll.

Sanders had the support of 47 percent of Democratic or Democratic-leaning voters while Clinton had 46 percent—a narrow gap that fell within the poll’s 2.5 percent margin of error. The national survey was conducted in the days before the Vermont senator handily defeated the former secretary of state in the Wisconsin primary, and it tracks other polls in the last week that found Sanders erasing Clinton’s edge across the country. In a poll that PRRI conducted in January, Clinton had a 20-point lead.

Trump is still in the lead, but Sanders and Clinton are tied Trump tops the Republican field, as he has for months. But fresh from a string of primary victories, Sanders has pulled into a statistical tie with Clinton among registered voters. Trump 37% Cruz 31% Kasich 23% Sanders 47% Clinton 46% Source | PRRI/The Atlantic April 2016 Poll Trump is still in the lead, but Sanders and Clinton are tied Trump tops the Republican field, as he has for months. But fresh from a string of primary victories, Sanders has pulled into a statistical tie with Clinton among registered voters. Trump 37% Cruz 31% Kasich 23% Sanders 47% Clinton 46% Source | PRRI/The Atlantic April 2016 Poll

Democrats are sharply divided by age and by party loyalty. Sanders is strongly preferred by younger voters, both women and men, while Clinton does better with older voters and those who closely identify with the Democratic Party. Sanders, by contrast, runs strong among weaker partisans and independents—a finding that has also been reflected in exit polls taken after people have already cast their votes.

The gap in party loyalty might explain why Clinton has been highlighting Sanders’s tenuous past connection to the Democratic Party in recent days. “He’s a relatively new Democrat,” Clinton told Politico’s Glenn Thrush in a podcast interview published on Wednesday. “I’m not even sure he is one.” She repeated the message in two separate television interviews later in the morning. “Senator Sanders, by his own admission, has never even been a Democrat,” she said on CNN. Sanders describes himself as a Democratic socialist and has won election in Vermont as an independent, although he caucuses with Democrats in the Senate. He considered running for president as an independent before determining he had a better chance of spreading his message in the Democratic primary.