WASHINGTON — Within hours of the Supreme Court accepting a case that could lead it to overturn or scale back a landmark abortion rights ruling, Senator Michael Bennet, a Colorado Democrat facing re-election next year, issued a dire warning to supporters: The fate of Roe v Wade is on the line. “We cannot move backwards,” Mr. Bennet said in a campaign statement. “Colorado was a leader in legalizing abortion — six years before Roe v Wade. I will...