Why is Obama involving the US in the current Egyptian crisis?

When hundreds of thousands of Iranians protested against the the anti-democratic Islamist regime in Iran he remained silent. But today he has condemned Mubarak's more secular regime to oblivion and supported the Islamist Muslim Brotherhood in their efforts to overthrow Mubarak. President Carter gave us the Islamist nation of Iran. It appears that another demcrat president is giving us another Islamist nation in Egypt.