Some Republicans are so desperate for Paul Ryan to step up as the next speaker of the House that they’ve started talking about retiring if he doesn’t, according to a group that works on behalf of the House GOP’s more moderate members. After Ryan, those members have no second choice or even a second tier of potential speakers, said Sarah Chamberlain, chief operating and financial officer for the Republican Main Street Partnership, a group that backs “mainstream” Republicans and plans to spend millions helping them protect their House seats in 2016. “Depending on how this shakes out, you may see...