Do the cop have the right to search your car at a sobriety checkpoint?

like you got pulled over at a sobriety checkpoint and the cop ask you to step out cause he figured you are drunk. You step out, took the test and the breathalyzer, and passed. Does he have to right to take anything out of your car without your consent, like a cup that has some liquid in it, say small volume of alcohol? but though, he never ask you what it was, and just took it assuming its alcohol.

ANSWER: If the cup you refer to was in plain sight and in reach of the driver the officer could reach in and check it to see if it contained an alcoholic beverage. REMEMBER - this was a sobriety checkpoint. He was checking for an 'open container' violation just the same as he would if he observed an open beer can or whiskey bottle.