WASHINGTON (AP) — Adam Schiff was in the audience at the 2018 Aspen Security Forum when a Microsoft executive mentioned an attempted hacking of three politicians up for reelection. It was the first that Schiff, then the top Democrat on the House Intelligence Committee, had ever heard of it.

Schiff said he thought it was "odd" that Congress hadn't been briefed. He got in touch with high-ranking officials in the intelligence agencies, and they didn't know about it, either. It turned out that Russian hackers had unsuccessfully tried to infiltrate the Senate computer network of then-Sen. Sen. Clai...