"Obama can sit there and let all the tax [cuts] lapse, and then the Republicans will have enough votes in the Senate in 2014 to impeach. The last year, he’s gone into this huddle where he does everything by executive order. He’s made no effort to work with Congress." Grover Norquist
First of all, allowing a tax cut bill to sunset per its own text isn't a high crime or misdemeanor. If the Republicans attempt to impeach the president over this, it'll be political suicide for them.
Secondly, the president will only allow the tax cuts for the wealthiest brackets expire. Everyone else will remain the same.