When most political followers hear “Republican senator” and “maverick,” they probably think of John McCain. He ran as part of a “team of mavericks” with Sarah Palin in 2008, after all. But whether or not McCain deserves the “maverick” label in general, he’s certainly not the Republican senator most likely to cross the aisle. That title belongs to Maine Sen. Susan Collins.

Collins has voted against President Trump more than any other Republican senator so far. While she has still voted with Trump’s position most of the time (85 percent), she’s the only GOP senator to vote with Trump less than 90 percent of the time so far. She was the lone Republican to vote against two of Trump’s Cabinet nominees (Betsy DeVos for secretary of education and Scott Pruitt for secretary of the EPA). And she was the only Republican to vote against the repeal of the stream protection rule for mining, even as some Democrats voted for it.

Collins’s record indicates that she may end up voting against Trump even more in months to come. From 1997 to 2015, Collins voted with her party a little less than 60 percent of the time in the average Congress. Only five of 225 senators in the average Congress (for whom we have a score) voted with their party less often during that period — and none of those five currently serves in the Senate. Throughout her time in office, Collins has consistently voted against her party’s position more often than the average senator.

So where might Collins differentiate herself in the rest of this Congress? Collins has already tried to stop repeal of the Affordable Care Act without a replacement. She co-introduced a replacement package that was middle-of-the-road enough to be called the “Obamacare Forever Act” by the Washington Examiner’s Philip Klein. Another area where Collins could be a thorn in Trump’s side is on immigration: Collins came out forcefully against the now-stalled travel ban, and she could be a vote against him on immigration were he to try to usher a bill through Congress.

The bad news for Trump’s opponents is that even if Collins does vote against the president on these issues, it may not be enough. On any vote requiring a bare majority, 51 Republican senators have voted with Trump 90 percent of the time or more.