The relevant part of the question is turnout. Will the Democratic base stay home? For that matter, if the candidate is weak, will the Republican base stay home?
The historic evidence is mixed, even for recent years. Turnout was almost steady in 1980 and 1984, an easy win for the incumbent. Turnout fell from 55% to 49% from 1992 to 1996, again in an easy win for the incumbent. But it rose from 51% to 57% from 2000 to 2004, when the incumbent was embattled and the election was close. So second term elections could go either way. The 2008 election was also a rounded 57%, but unrounded it went up a full 0.68%. That means turnout has increased for four straight elections and was the highest since 1968.
Why has turnout increased? My guess is that two trends are pushing in the same direction.
One is that the country is increasingly polarized. This has large downsides, as we just saw with the budget bill, but polarized voters are more likely to turn out to support their parties. The hard-fought 2004 election, with a close vote, did see increased turnout.
The other is that we live in a media bath today that is unprecedented. It was a lot easier to turn off national politics a generation ago. Today it’s everywhere, in every form of media.
Estimates are that each side will spend a billion dollars on the 2012 campaigns. People are far more likely to complain about the assault of ads than to say that they don’t know what’s going on. People may hate the ads but I know of no evidence that says that people vote less because of them. There’s always a gulf between what people say and what people do.
I’d wouldn’t be surprised if turnout was a bit lower in 2012 than 2008, but I would be surprised by two things. One, if the percentage difference was large, and two, if the lowered turnout was all on one side. The 2010 election was decided because Democrats stayed home, and the party leadership will be determined not to let that happen again.
A lot will depend on how the Republican challenger does. Both Mondale in 1984 and Dole in 1996 were considered to be poor campaigners, although their parties had next to no chance to win no matter what. Kerry was hardly a fireball on the campaign trail. Possibly a better candidate could have won, but beating an incumbent is always hard. That will be true in 2012 as well. Despite the bashing Obama takes, his numbers consistently beat any named individual candidate. If the Republicans don’t run an absolutely perfect campaign with a charismatic candidate and perfect strategy there’s no reason to think they can oust a sitting president. It happened with Reagan and Clinton, true, but you can apply charisma to each of those names. Romney doesn’t have it. Do any of the other candidates?
Anyway, low turnout by disgruntled Democrats is unlikely. There will be a billion reasons not to expect that by November of 2012.