Even some self-described conservatives are showing a willingness to support Biden. The former vice president is winning 22 percent of their vote against Trump. Trump carried 81 percent of the conservative vote in 2016, but is now holding a 71 percent job approval among them.

And while Trump has maintained his hold on the Republican Party—boasting an 87 percent approval rating among intraparty voters in the Fox poll—it’s worth noting that fewer voters self-identify as Republicans these days. Some disaffected Bush and Romney supporters now consider themselves independents. Trump’s approval among independents in the Fox poll? A dismal 29 percent.

For a president who has relied on a base-first strategy at all costs, hoping to win reelection without courting new voters, even the slightest slippage among rock-solid Republicans is alarming. The revelations from former Trump national security adviser John Bolton’s new book may not matter to Trump’s hardcore base, but there are plenty of softer Republican voters already close to breaking away.