Yet Ed Kavanaugh’s career may shed light on why conservatives are so enthralled by his son’s nomination to the Supreme Court. He spent more than two decades in Washington as a top lobbyist for the cosmetics industry, courting Congress and combating regulations from the Food and Drug Administration and other agencies. (Among his hires for legal work: John G. Roberts Jr., now the chief justice.)

In current parlance, as an old friend put it, the elder Mr. Kavanaugh and his associates were “swamp creatures,” using money and connections to fend off demands for safer products and greater transparency about ingredients. He was a golf partner of Tip O’Neill, the longtime Democratic House speaker, who weighed in to support Martha Kavanaugh’s nomination to a judgeship. His compensation package was $13 million in 2005, his last year at the Cosmetics, Toiletry and Fragrance Association, records show.

Now Brett Kavanaugh, should he be confirmed, will cement a solid pro-business majority on the nation’s highest court, advancing Mr. Trump’s aim of dismantling the regulatory state, liberating industry from what he sees as burdensome rules.