A group of state legislators who support the health law have discussed what they could do to replace the insurance mandate, if the court strikes it down, said Karen Keiser, a Democratic state senator in Washington who chairs the group. Possibilities for replacing a federal mandate include the “politically difficult” route of passing state versions of the mandate, or replacing private insurers with government-run coverage in some states, Keiser said. “It’s much more likely that states would step in and take it on because it seems the Congress is really at impasse,” she said by phone. In states that choose not to act, she said, “a large number of Americans would be left out and left behind.”