If there is waste, then the proper channel to address is through Congress which controls the budget. The executive is not a dictator and cannot impound or dissolve congressionally appropriated funds.
The GOP controls both houses and could easily do this if they were so convinced. Instead they're laser focused on cutting taxes on billionaires to the tune of $4 trillion dollars
And even supposing that an administration doesn't fully trust Congress (or its ability to execute through parliamentary gridlock), there are a bunch of people in the executive branch whose whole-ass job it is to investigate this stuff, and could legitimately be directed to shift their priorities without Congressional approval. Oops, scratch that; there were a bunch of people with that job. [1]
Not only that, but that same Republican controlled congress has seemed more than happy to throw their hands up and let Trump stomp all over their authority. I guess because it hurts the Democrats more than them right now.
The GOP controls both houses and could easily do this if they were so convinced. Instead they're laser focused on cutting taxes on billionaires to the tune of $4 trillion dollars