President Donald Trump flexed his grip on the GOP base in Indiana on Tuesday, vanquishing a majority of the Republican state senators who had dared cross him on redistricting.

It was a show of force in the year’s first major test of Trump’s power over the GOP. Trump aligned groups dumped millions against the eight GOP lawmakers who blocked his effort to gerrymander the state. And on Tuesday night, at least five lost reelection.

Trump’s loyal and energized supporters turned out to punish the incumbents, showing that his endorsement remains the gold-standard of GOP politics. That’s a bright flashing red warning to any Republicans who might be eyeing a break from Trump as he approaches the back half of his second term in office.

The victories came after a combined $13.5 million in spending poured into typically low-profile state Senate races, most of it for Trump’s candidates.

“It’s a sign that the party’s ready to follow the president on this and also turn over a new leaf, and get younger, newer leaders in the state Senate,” said David McIntosh, president of the Club for Growth, which put more than $2 million in the race.