WASHINGTON — U.S. House Speaker Paul Ryan on Friday acknowledged the unthinkable for a Republican leader: he could not deliver the votes to repeal and replace Obamacare, even though he and his fellow Republicans had vowed to do so for seven years.Nevertheless, Ryan’s job did not seem to be under immediate threat, at least not in the House of Representatives he leads.Ryan’s long-time news media nemesis, the website Breitbart, said Republicans were “openly discussing” finding a replacement for him after he pulled a bill to roll back Obamacare from the House floor just minutes before an intensely awaited final vote.