President Barack Obama, a Democrat, said he’ll nominate a successor to the U.S. Supreme Court Justice Antonin Scalia, but Republican leaders and presidential candidates have said the replacement should be picked by the next president. The nominee must win confirmation from the Senate, which is controlled by Republicans.

So, Obama has some options: He could pick a compromise candidate — one who is more conservative than his previous nominees but less conservative than Scalia — and dare Republicans in the Senate to reject someone whom they would likely confirm if not for election-year politics. Or he could pick a liberal candidate to rally the Democratic base with the goal of helping his party retake the Senate in the 2016 election, recognizing that a nominee perceived to be liberal would not likely make it to the court.

A nominee perceived to be apolitical or middle-of-the road ideologically — but with an exemplary legal background — could create a dilemma for U.S. Sen. Susan Collins, a Republican from Maine who takes great pride in her reputation as a moderate. If hard-line conservatives in the Senate continue to insist that any Obama nominee be rejected — a position that campaigning Democrats would use to portray the Republicans as obstructionist, partisan and undemocratic — Collins would find herself torn between party loyalty and her stated commitment to moderation and effective governance.

Collins supported Justices Sonia Sotomayor and Elena Kagan — Obama’s two nominees to the Supreme Court — in 2009 and 2010.

In a statement to Politico, Collins came perhaps the closest with breaking with her caucus, criticizing Republicans and Democrats for “speculating so soon” about a nominee after Scalia’s death. 

“More than any other appointment upon which the Senate is called to pass judgment, nominees to the Supreme Court warrant in-depth consideration given the importance of their constitutional role and their lifetime tenure, Our role in the Senate is to evaluate the nominee’s temperament, intellect, experience, integrity, and respect for the Constitution and the rule of law,” Collins said in an emailed statement to Politico.

She’s at least leaving the door open to supporting Obama’s nominee, and her posture going forward is worth watching.