By Dustin Volz and David Lawder WASHINGTON (Reuters) - Former U.S. vice presidential candidate Sarah Palin vowed on Sunday to help unseat Paul Ryan, the top Republican in the House of Representatives, because of the his refusal to endorse presumptive Republican nominee Donald Trump. Palin, the former Alaska governor and Trump supporter, endorsed conservative businessman Paul Nehlen, who is challenging Ryan, the House speaker, for his congressional seat in the Wisconsin Republican nominating contest on Aug. 9.
