A more thorough explanation:

Clinton v. City of New York is a Supreme Court case that dealt with the Line Item Veto Act. This act allowed the President to veto a single appropriation or tax benefit within a large appropriation or tax bill without having to veto the entire bill. The act was intended to limit government spending.

However, the Supreme Court ruled that the Line Item Veto Act was unconstitutional because it violated the Presentment Clause of the Constitution. This clause requires that a piece of legislation passed through both houses of Congress in its entirety before being signed or vetoed in its entirety by the President. By giving the President the discretion to accept or reject parts of the bill, the Act would have allowed the President to amend the laws that were presented, which would have gone against the Congressional purpose.

For example, if Congress passed a bill that included funding for a new highway and a tax break for small businesses, the President could veto the tax break without vetoing the entire bill. This would have given the President too much power to change laws without going through the proper legislative process.

In summary, Clinton v. City of New York struck down the Line Item Veto Act because it gave the President too much power to amend laws without going through the proper legislative process.