Voters in left-leaning Washington state and Colorado have approved measures designed to ban transgender athletes from participating in school-sanctioned sports.

Measure 638 in Washington, which had more than 56% of the vote, will prevent students who were assigned male at birth from participating in sports designated for female athletes. The measure also requires athletes wanting to play in female sports to produce a statement from a health care provider verifying their gender.

Proposition 134 in Colorado will require educational institutions and athletic associations to assign sports as male, female or coed.…