The military budgets of most countries, ours included, tend to go in one direction: up. National security is an easy case to make, a few politicians want to be seen as weak on security by opposing spending on arms.
Paul Holden, who has covered many arms sales, finds flaws in the logic and even the facts used by people who seek to bolster arms spending. Holden is both editor and principal author of Indefensible: Seven Myths that Sustain the Global Arms Trade. His interview is from 2017; his case is more or less current.