Blake was the mayor of Washington when British troops laid siege to the city on August 24, 1814, as part of the War of 1812. He put the city on alert a few days before the siege, insisting that "I would exert myself to the last moment and agree to die in the streets rather than give up the city, but, if all resistance was given over, and our military abandoned it, I would then also leave it and not surrender myself a prisoner to the enemy." It was Blake who urged Dolley Madison, the First Lady, to flee Washington before the British arrived. He then rounded up men to defend the city, so occupied with its fortification that his wife and four children were forced to make escape on their own.