We can also reapproproate tax dollars from failed programs to science.
Who is we? And by what standard is "plenty" measured?
Less tax revenue will result in less accomplished by government; it's inevitable. Already, important programs are cut in the US and UK. For example, as people were dying the US Congress wouldn't fund Zika virus research, and CDC (or NIH) shifted resources from Ebola research and/or treatment. The US military has clearly stated they cannot defend the country and accomplish their mission with current funding.
People can always claim they can 'trim the fat', etc.; it's just words; a promise of something for nothing, government services without having to pay for them. It's been used by politicians for as long as taxes have existed.
I'd be interested in serious research showing where such inefficiencies exist and what can be done, but the claim by itself isn't substantive.