Last year thousands of anti-abortion activists descended on Washington for their annual March for Life, eagerly hoping that President Trump's second term would accelerate aggressive actions to end remaining abortion access in the United States. This year, they arrived on the National Mall with their usual upbeat signs and prayers — but many were also carrying a gnawing sense of frustration. Even as abortion opponents have gained ground and put allies in key policymaking positions, Mr. Trump has at times also infuriated them, exposing fractures among a group whose support has been critical to his success for the past decade...