And just so it's clear, the White House was told this by (now fired) Acting Attorney General Sally Yates late last month:
So, the White House has known about this for weeks, but didn't ask Flynn to resign until it became public. This is not looking good for Trump and cronies.The acting attorney general informed the Trump White House late last month that she believed Michael Flynn had misled senior administration officials about the nature of his communications with the Russian ambassador to the United States, and warned that the national security adviser was potentially vulnerable to Russian blackmail, current and former U.S. officials said.