In only one Congress out of 10 since 1997 (the 105th) has McCain voted with his party more often than the median senator. Before that, he’d done so in three out of five congresses. McCain was at his most maverick-y during the early and middle part of President George W. Bush’s administration. From 2001 (107th Congress) to 2006 (109th Congress), McCain voted with his party 79 percent of the time; the median senator voted with his party 93 percent of the time. McCain’s maverick ways fell off during the early years of President Barack Obama’s administration, but McCain was, on average, 10 percentage points more likely to vote against his party than the median senator in the second half of Obama’s tenure.

And it’s not just that McCain is voting against his party on unimportant issues: McCain has been more willing to vote against the more conservative position on key votes in the past 20 years. McCain voted against the Bush tax cuts, for reducing greenhouse emissions and for funding Obama’s executive action providing federal benefits to immigrants who are in the country illegally, in addition to arguing against torture. You can see that McCain’s transformation on key votes (again measured by the American Conservative Union’s scorecards) matches up with when he began to buck the GOP on party-line votes overall: Just before his first run for the presidency in 2000…

So is it fair to say that McCain has stepped up his maverick game since the late 1990s, with a few breaks along the way? Well, not exactly. Much of McCain’s maverick image in recent years may simply be grade inflation. As polarization has taken hold, and Democrats have become more liberal and Republicans more conservative, a position that was reliably conservative 10 or 15 years ago now looks moderate. Maybe McCain didn’t change; maybe his colleagues did. Indeed, McCain has voted with his party 86 percent of the time on all party-line votes in the average Congress since 1997. That’s little different from his average of 88 percent from 1987 to 1996. But compare McCain’s slight drop in voting with his party to the rising polarization in the Senate. The median senator has voted with his or her party 93 percent of the time in the average term since 1997. From 1987 to 1996, it was 88 percent.