Some major Democratic donors told the largest pro-Biden super PAC that their pledged contributions, worth about $90 million, were on hold while President Biden remains on top of the ticket, according to two people briefed on the conversations.

The decision to withhold such enormous sums of money offered one of the most concrete examples yet of the concerns many Democrats have about Biden’s candidacy. Two weeks after the president’s poor debate performance, several elected leaders and party strategists have grown increasingly alarmed that Biden’s presence on the ticket could transform some blue states into contested battlegrounds.

But Biden has been adamant that he will remain in the race. He tried to use a nationally televised news conference last night to convince the American electorate — and Democratic leaders — that he can and will defeat Donald Trump in the November election.

During the event, he demonstrated a grasp of the issues and seemed comfortable during a long discourse on foreign policy. He was mostly steady, if not exactly compelling.

Still, a few more Democrats and a major environmental group today made public their calls for Biden to step aside. In total, 19 House Democrats have called for a new nominee, and more were expected to come out of the woodwork.

Tonight, Biden is holding an event in Detroit, where he will attempt to turn attention back to Trump’s policies.