When Secretary of State Hillary Rodham Clinton absolved out of a gilded allowance in the Capitol on Wednesday, afterwards a breakfast with lawmakers, she said she was amused to be aback in accustomed surroundings.But the break was annihilation but festive. Mrs. Clinton was on a mission to save one of President Obama’s few adopted action victories: an arms-control accord with Russia aback jeopardized by the abnegation of a distinct Republican to acquiesce a vote on the alliance in the Senate this year.It is a role Mrs. Clinton expects to comedy frequently in advancing months, as the White House girds for a added adverse Congress angled on arduous or alike blocking the Obama administration’s adopted action agenda, whether accoutrements control, the Middle East accord process, the war in Afghanistan or the acting beat to Cuba.With eight years in the Senate, bisected in the minority, and a acceptability for accepting forth with Republicans, Mrs. Clinton is able-bodied able to be an agent to Congress, several administering admiral said. But the draft to the alleged New Start accord — admitting two dozen affairs and buzz calls by Mrs. Clinton — shows that her abilities may not be abundant in this antagonistic political environment.