One big reason the deficit is going to get so big is Democrats voted with Republicans to prevent the tax cut bill from triggering the Paygo law Democrats wrote to prevent the deficit from going up.
I suspect that if Democrats ever get to 60 votes again they will write a very different Paygo law, instead of one that automatically cuts Medicare and other entitlements they support.
Last year likely would have gone very differently if the Paygo law, say, automatically hiked taxes on billionaires if Congress increased the deficit.
