Indian tribes that run casinos were major backers of Sen. Adam B. Schiff’s last campaign — and the California Democrat is now delivering for them, with new legislation to keep them from having to face competition from online betting platforms. Mr. Schiff’s legislation would prohibit online prediction markets such as Kalshi and Polymarket from issuing prediction contracts on sports events or casino games. He said the national platforms end up being a workaround for people who live in places