Obama is the anti-christ.
The anti-christ will rule peacefully for 3.5 years, which is the first half of the tribulation.

The second half of the tribulation will be bad....very bad.

Obama's term runs out after four years.
It currently looks like he won't be re-elected, but 3.5 years into his presidency and just 6 months before his terms runs out, something is going to happen. This something will be martial law, which means that the constitution will be suspended.

Maybe martial law will be declared after a failed assaination attempt on Obama's life. Iran will get the blame. Obama's head wound will be healed, except he won't be himself any more.

Obummer is the last American president.

The date to look out for, is the 21st of July 2012. This is exactly 3.5 years after his inauguration.