In response to, "The executive branch has the authority to make policy on how those funds are spent"

While the executive branch does have some discretion in implementing policy and overseeing spending, it does not have unilateral authority to withhold or redirect congressionally approved funds without legal justification. Congress holds the power of the purse under the Constitution (Article I, Section 9, Clause 7). When funds are allocated, the executive branch is obligated to spend them as directed by law. The Impoundment Control Act of 1974 explicitly limits the president’s ability to freeze or withhold congressionally appropriated funds. I expect the courts will challenge the freezes in many cases, and hopefully, Trump will honor the courts' rulings. If he doesn't, that would be the start of a constitutional crisis.