They were predicting a $12 trillion net deficit between 2017 to 2027. Discretionary spending would decline by around 10% while mandatory spending would increase substantially. Discretionary spending's been trending downward as mandatory spending increases. https://www.cbo.gov/system/files/115th-congress-2017-2018/reports/52480-ltbo.pdf
That was before this tax bill, assuming moderate average growth and no change in the laws (the usual CBO assumptions).
So now we're livid that the net deficit's predicted to be around $13.5 trillion, because the order-of-magnitude-bigger $12 trillion was no big deal. In fact, that level of deficit spending was a big improvement over what was, actually, lower levels of deficits before 2009. I find it all grimly amusing.
"Mandatory spending" is, for the purposes of that report, Medicaid, Medicare, Social Security, CHIP, ACA subsidies. Not military. Not infrastructure. Not additional entitlement programs like SNAP. Not education. Not NHS or EPA or NIH.