"Our movement cannot forsake the foundational commitment we have to security, to limited government and to life," Pence said in the speech on Wednesday.
"But neither can we allow our movement to be led astray by the siren song of unprincipled populism that is unmoored from our oldest traditions and most cherished values."
Pence voiced no personal criticism of Trump and only referred to him by name as "a man I deeply admire." But Pence made clear he had timed his remarks in anticipation of a Republican resurgence in the midterm congressional elections in November that, he predicted, would restore control of Congress to the Republican Party.
"We are 20 days away from the great American comeback: Twenty days from now I do believe we will have majorities in the House and in the Senate," he said.
Pence also demanded that if the Republicans win control of both chambers of Congress in November, they should use that power to comprehensively outlaw the practice of abortion in every one of the 50 US states.