ARIZONA is America's 15th largest state by population, but it is a fair bet that Jan Brewer, who announced this morning that she would not seek re-election in November, ranks rather higher on the list of its best-known governors. Vaulted to office in 2009 to replace Janet Napolitano, whom Barack Obama had appointed homeland-security secretary, and re-elected a year later, Mrs Brewer rapidly turned herself into the Marmite of governors. Red-blooded conservatives loved her uncompromising approach, perfectly encapsulated in a famous photo of the gubernatorial finger being jabbed in the presidential face in January 2012. They also loved the way she held strong in the face of fierce opposition, both local and national, to SB 1070, a controversial law she signed in 2010 that allowed state officials to enforce federal immigration law, but that critics charged encouraged racial profiling. Indeed, she is still fighting to implement some of its provisions voided by the Supreme Court in 2012. Liberals and Latinos hated her for the same reasons. But more recently Mrs Brewer has given hardliners on her own side cause to distrust her. Last year she waged an aggressive, but ultimately successful, battle to expand Medicaid under Obamacare (or "Obrewercare", as some of her foes quipped); a move seen as almost treasonous by many Republicans in the state legislature they dominated, despite (or perhaps because of) the federal dollars it attracted. And then, just two weeks ago, the governor not only vetoed SB 1062, a bill passed by the legislature that would have allowed employees of private businesses to cite religious beliefs in refusing to serve gay customers, she did so in surprisingly forceful language. Social conservatives, who thought the governor was one of their own, howled in dismay (and continue to howl).

These reverses, and others, led to a growing disconnect between the Jan Brewer America thought it knew, and the Jan Brewer Arizona decided it did know. A recent Politicoarticle on the governor quoted a Phoenix Tea Party leader thus: "The further you get out of Arizona, the more, if you ask people in the Tea party if she’s a conservative, they will still say yes. But as you get local, they will say, no … Honestly, no.” Mrs Brewer has never been media-friendly, as this correspondent can attest, and her halting public persona does not lend itself to easy analysis. In an interview after her announcement today, she pledged to support pragmatic Republicans over "ideologues".

A complicated governor, then, in a complicated state. Arizona remains firmly Republican. Until recently that was also true for many of its neighbours. But the mountain states are changing, perhaps quicker than any other region in the country: as this map of the 2012 presidential-election result shows, bar the conservative Mormon enclave of Utah to its north Arizona is now surrounded by Democratic-leaning states, and the demographic forces that are turning the west blue—broadly speaking, inward migration of young, liberal-minded folk, and a growth in Latinos—are also changing Arizona.

Older migrants, many of them retirees from colder climes, have helped to maintain Arizona's Republican tilt, for now. (Indeed, Mitt Romney performed marginally better in Arizona in 2012 than did John McCain, an Arizona senator, in 2008.) But Latinos now make up almost one-third of the state's population (if not its electorate), and their turnout increased by 37% between the 2008 and 2012 elections. In 2012 they were even less likely to vote against Mr Romney than their national counterparts. Democrats are hungry for Arizona's 11 electoral-college votes, and have not ruled out nabbing them in 2016.

Moreover, immigration, the issue for which Arizona's conservatives have become best known, may be losing its bite. For much of the last decade Arizona was on the front line of America's illegal-immigration problem, as increased enforcement along the Californian border pushed the problem east. Figures like Joe Arpaio, "America's toughest sherriff", proved adept at exploiting locals' concerns. But the numbers attempting crossings have tumbled; and of those that are still trying, many have shifted further east, to Texas.

So it is not clear where Arizona's post-Brewer future lies. As a Western state, it has a taste for libertarianism not shared by its fellow conservative states in the south-east: gay-marriage and marijuana-legalisation advocates see it as fertile ground. Demographics are slowly pushing it leftward. Partisan affiliation is falling, but registered Republicans still heavily outnumber Democrats, and independents lean rightwards. The governor's race looks wide open; nine Republicans are running (probably a safe bet this guy won't make it). And do not rule out a Democratic victory; Ms Napolitano pulled it off in twice. Arizona looks set to maintain its capacity for surprise.