The President tapped three pots of money to build more border wall than Congress directly funded with appropriation.
Each of the three - Treasury Asset Forfeiture funds, DoD Counter-Narcotics funds, and Military Construction (MILCON) funds - were authorized for his use by separate laws.
The $3,6 billion of MILCON money, can only be diverted for such use under the National Emergencies Act of 1976, which the President cited in his declaration of emergency in February.
That law allows Congress to override the President’s declaration, with a two thirds vote of both Houses (or a simple majority, if the President does not veto it). The law also allows Congress to re-vote on overriding that emergency declaration every six months, while it continues.
It just came up for that routine re-vote, and even fewer voted to override this time, than the last time - Congressional opposition weakened, in recognition of the overcrowding (or possibly their cynical gauging of the politics of the issue).
So nothing to worry about, the President will veto this one, just like the last one. He will see them again in six months (and likely again six months later, as the election nears - which might then change the calculations of legislators).
Thanks for the information.