He thinks that Obama violated his oath of office.
Check it out:

Many Republicans watched the State of Union Address with clenched teeth, as Obama once again made threats and promises to act without congress, and beyond the law “whenever and wherever” he could.

Finally, Representative Steven Stockman of Texas made the decision to walk out of the address, claiming that he was upset after “hearing how the president is further abusing his Constitutional powers” and watching the president blatantly ignore “clearly-defined boundaries of the Constitutional separation of powers.”