Republicans have already started bellyaching about the president canceling his charm offensive and sticking a thumb in their eye by promoting the person they view as the main face of the Benghazi mess. But there’s absolutely nothing they can do to stop Barack Obama from installing Susan Rice as his top national security adviser.

The job is the most important post in the entire executive branch (other than White House chief of staff) that doesn’t require Senate confirmation. So Rice’s move — a sooner-or-later sure thing ever since her secretary of State ambitions were quashed this winter — can be carried out whenever Obama decides it’s OK for her to leave the United Nations.

That probably won’t be until her successor as U.N. envoy is confirmed. And it may take some time, and at least one contentious hearing, before Samantha Power gets to return to government service and move to New York. A fight over her confirmation looks to be a proxy for what irks the GOP about administration foreign policy.

There is little about the 42-year-old Power’s résumé that would pose obvious concerns to senators from either side. But when she testifies on her own behalf on Capitol Hill, the hearing is sure to become a forum for all manner of Republican skepticism about how the Obama administration is conducting international affairs.

It will also provide another outlet for rehashing everything the GOP doesn’t like about Rice and the faulty explanations she and others gave about the terrorist attack in September, which killed four Americans at the consulate in Libya’s second-biggest city.

Power has spent her entire adult life writing about and setting policies to do with human rights and genocide, arguing forcefully for an American foreign policy that uses moral grounds as a basis for military intervention.  She won the non-fiction Pulitzer a decade ago for “A Problem from Hell: America and the Age of Genocide.”

As a result, senators on both sides will press her hard to say whether she would advise the president to act more assertively to change the situation in Syria, where the government has killed tens of thousands of civilians, or to take a different view about the situation facing Palestinians in Israel.

When Obama was a freshman senator from Illinois, Power was a foreign policy fellow on his staff. And she was the senior foreign policy adviser on his presidential campaign until she referred to his rival for the Democratic nomination, Hillary Rodham Clinton, as “a monster.” Recalling that incident at the hearing will certainly give way to questions for Power about how she though Clinton did as secretary of State.

Power returned to the Obama fold after his election and, until February, was the National Security Council member in charge of multilateral affairs and human rights policy in the West Wing. In that post, she was a key player in the Obama decision to intervene in Libya. (She also ended up marrying another senior administration official, Cass Sunstein, who was in charge of setting regulatory policy but has now gone to teach at Harvard.)

Her time in the White House presumably exposed her to some of the deliberations about the response to the Benghazi attack, and so she will be pressed for any insights that might support or rebut GOP suspicions that the administration was inconsistent through incompetence, at best, or because of a  cover-up.

Obama will formally announce his plans for shuffling his national security team in the Rose Garden this afternoon. Rice will be replacing Tom Donilon, but no earlier than next month, after the president returns from overseas trips to Europe and Africa and has this weekend’s summit in California with Chinese President Xi Jinping, a meeting that Donilon worked to arrange as part of his priority of shifting U.S attention more toward Asia.