Judge Brett M. Kavanaugh saw the importance of saying “no” while working as associate counsel for President George W. Bush, he told students at Marquette Law School this month.

Being a judge on the U.S. Court of Appeals for the District of Columbia Circuit similarly requires “backbone,” he said.

A favorite of conservatives, Kavanaugh, 51, has had no trouble saying “no” to the Obama Administration on high-profile environmental matters.

A prolific “feeder judge,” Kavanaugh’s clerks have been hired by more than half of current Supreme Court justices, both conservative and liberal.

Power Player.

Kavanaugh’s role on arguably the second...