Trump’s legal troubles are mounting. And his support is consolidating.

The lawsuit filed Wednesday in New York accusing Donald Trump and three of his adult children of fraudulent financial practices was met with fresh outrage on the left.

Jaime Harrison, the Democratic National Committee chair, suggested with a GIF that New York had produced the receipts on the former president. Michael Beschloss, the presidential historian, wrote he’d “never seen anything remotely like this in history of American Presidency.”

But to Republicans, after Trump’s presidency and its aftermath, the bombshell was simply more of the same. Just as they rallied around Trump when the FBI searched his...