Not an American here, but doesn’t Congress pass budgets? Everyone always blames the president but as I look in from the outside, it’s entirely the house and the senate who bungle things.

I've had the same question for a long time and I suspect the answer is something like "the executive is still the one doing the analysis and making the proposals" - presumably Congress doesn't just allocate with complete disregard for what the executive requests. If the executive requests less then it (usually) gets less. But I'd definitely appreciate a more satisfactory answer.