Yes, it's buyer's remorse and it will probably be one of the deciding factors in the race this year.

Gallup:

Eighty-six percent of voters who say they voted for Barack Obama in 2008 are backing Obama again this year, a smaller proportion than the 92% of 2008 John McCain voters who are supporting 2012 Republican candidate Mitt Romney. Nine percent of 2008 Obama voters have switched to supporting Romney this year, while 5% of McCain voters have switched to Obama.

The results are based on July 23-29 Gallup Daily tracking with more than 2,000 registered voters who reported voting in the 2008 election. Of these, 48% said they voted for Obama and 42% McCain, with the remaining 10% saying they voted for another candidate or not disclosing their vote choice. However, the six-percentage-point advantage in reported voting for Obama is similar to the actual seven-point edge he had over McCain in the final 2008 returns, 53% to 46%.

Obama and Romney have been tightly matched so far this year, with the two generally tied or one having a slim one- or two-point advantage among registered voters in Gallup Daily tracking.

Thus, it follows that fewer voters are supporting Obama this year than in 2008. But the race remains close because Obama's margin in 2008 was large enough that he could still be tied or in the lead this year if his support is a few percentage points lower.

The data do underscore the high degree of party loyalty in voting across the last two elections. All told, 79% of registered voters are supporting the same party's candidate in 2012 as in 2008. That figure understates the true degree of party loyalty because the loyalty of the substantial minority of voters who did not report their 2008 vote choice cannot be computed. Among those who say they voted for either Obama or McCain in 2008, 89% are supporting the same party's candidate in 2012, leaving 11% who are either supporting the other party's candidate (7%) or are undecided (4%).

It is truly amazing that Obama and Romney are going to spend at least a half a billion dollars over the next 3 months in order to try and capture a miniscule number of votes. With 90% of the country having made up its mind, that last 10% -- concentrated in a few swing states -- will determine who is president.