This was already a game-changing week in a Syrian crisis that seemed intractable, with rebel soldiers taking the battle to the streets of the Damascus.
But the bomb attack on national security headquarters in the capital this morning truly strikes at the heart of the Assad regime.
Defence Minister Dawoud Rajha was a key member of his inner circle.
A former army chief of staff, he was one of the small number of trusted aides directing the Syrian army's response to the uprsing.
A second member of that elite, Assef Shawkat, Assad's brother-in-law, also seems to have perished in the blast.
The bomber was apparently a bodyguard, which is evidence of how far and how deeply the oppostion has penetrated.
The Free Syrian Army claimed responsibilty for the blast. They had promised "surprises'' during what they now bill as the battle for the liberation of Damascus.
To adapt a Churchillian phrase, this week already looked like the end of the beginning of the struggle for Syria.
Perhaps this is, finally, the beginning of the end for Assad himself.