Taxpayers pay in regardless of how the money is spent. The total budget + borrowing when done = money available. Spending out of that pile on various things occurs. What you, or I consider waste, or poor choices is going to vary. For a comparison on the importance of some line item in a budget the only thing that matters is its percentage to the whole. It is a separate debate as to whether a line item is a good or bad idea.
There are two ways for Mandani to raise money. He can tax it, or he can borrow it.
There are three ways for the federal government to raise money. They can tax it, they can borrow it, or they can print it.
Borrowing means issuing a bond. You must entice people to buy that bond by offering an interest rate. This means the government must LOSE money by paying for that bond, and the interest. It must raise MORE money to cover the cost of the loan. Like any consumer living on tick, this can only go on so long. The result is a debt crash. People left with those bonds are hung out to dry. They do not get paid, and the government defaults.
If they tax too much, a revolt is sure to follow. Fleeing the area is one form of revolt. A tax crash.
If they just print it, you get inflation. That is the direct cause of inflation. Because the dollar has been devalued by printing, you must print more. This in the end results in a cash crash. The money becomes effectively worthless and people choose another form of currency. NOTHING the government can do will stop it.
ALL fiat currency is subject to this. The United States is better off than most any other nation, but it is headed there just the same. It has already hit Japan, Brazil, Mexico, and now China. NOTHING makes the United States immune.
For Mandani, he is stuck requiring huge amounts of cash to implement his socialistic programs, including the communistic grocery store. As with all socialism, it must steal wealth from productive individuals to pay for the socialism. For this reason, socialism always fails. Sooner or later, it runs out of people to steal from.