Democrats are supposedly happy about Mitt Romney’s choice of Paul Ryan because it helps them transform the election from a referendum on the last four years (which Obama cannot win) into a choice about the next four (which Obama hopes to win by labeling Romney-Ryan “extreme” — the word used three times by David Axelrod in his mass email yesterday).

But the referendum on Obama has already been held. The 2010 election was a personal rebuke (Obama referred to it the next day as the “shellacking … I [took]”); two years later, the verdict on his performance is, if anything, worse: his approval rating among likely voters is at 45 percent, and 43 percent of them “strongly” disapprove – the same “strongly disapprove” percentage George W. Bush had in January 2009; likely voters want ObamaCare repealed by a lopsided majority (55-39); and Obama has been reduced to claiming he always said things would take much longer to get better, when he never said anything of the sort.

Paul Ryan has long argued that the 2012 election needs to be about a “choice” — not to win it, but to make it worth winning. In his eloquent November 12, 2001 address to the Claremont Institute, entitled “Our Churchillian Moment,” he concluded as follows:

[N]othing is more predictable than the danger rushing upon us from the oncoming fiscal train wreck. There is still time to take the actions needed to reduce spending, reform our tax code, take control of the debt, restore economic growth, and repeal and replace the president’s health care law … The biggest problem is timidity, lack of political will, fear of losing the next election for speaking truth …

Look, Republicans didn’t always get it right as a party ourselves. But if there ever was a time to gather our political courage and reclaim our ideas, it is now. The country is facing a very precarious moment. Your leaders owe you a real choice … It is our moral obligation, as elected representatives, to give the American people this choice.

Unseating an incumbent president always involves both a referendum and a choice. The verdict on Jimmy Carter’s performance was clear in 1980, but voters still had to be convinced that Ronald Reagan (whom the Democrats had demonized as “extreme”) was the right alternative; the election was close until after the debates. In 2012, the verdict on Obama has long been clear; with his pick of Ryan, Romney has now brought a similar clarity to the choice the voters face.