Reading between the lines this statement is has a number of consequences. My reading of what he said is this: Threatening, bombing or taking Tbilisi International Airport (giving away some American, likely satellite, intelligence) is a Rubicon moment. If Russian forces act against the airport, it will be taken as crossing the Rubicon. Bush made no mention of likely consequences, and why should he?… it would be giving away his hand.
The message to Putin was clear: Withdraw, do not attack the airport, do not overthrow the Georgian government. Accept the EU-brokered ceasefire. Leaving the consequences of Russian rejection to the imagination is an entirely natural response.