It happens all the time. A president says, "We can't wait for the free market to bring about this change, Congress must act."
The next president says "We can't wait for Congress to act and declare war, I'm going to send in the military under my inherent powers as 'Commander-in-Chief'"
Then a president says "We can't wait for a country to show itself as hostile, there are people there who say they dislike us, we're going to invade."
Then the next president says "We can't wait for a jury to convict this American, we need to assasinate him now."
We Can't Wait may be Mr. obama's new slogan, but it's not a new concept. President's have been using this excuse to expand their authority and weaken our Constitution since it was ratified.