Sarah Palin, a former Alaska governor and the Republican nominee for vice president in 2008, said Friday that she was entering the race for Alaska’s lone congressional seat, marking her return to national politics after she helped revive the anti-establishment rhetoric that has come to define the Republican Party. She will be joining a crowded field of nearly 40 candidates to fill the House seat left vacant by Representative Don Young, whose unexpected death last month has spurred one of the largest political shifts in the state in 50 years. Ms. Palin said she planned to honor Mr. Young’s legacy,...