The $2 trillion is the increased revenues that they claim will come from all the super-duper economic growth unleashed by their tax cuts. This is fundamentally non-credible.
Tax cuts sometimes lead to increases in economic growth, particularly if you're starting from a very high tax level (we aren't). Or if you're seriously underperforming what it seems like you should be able to do (we're not - we're on a long-run trend of slowing growth, and past tax cuts have done nothing to stem that trend).
So that's why the $2 trillion doesn't exist.
The first place the White House proposes to use the non-existent money to finance the tax cut they claim will produce it.
But then it also wants to use the same money to pay for balancing the budget.
White House budget director Mulvaney isn't exactly denying the criticism:
"I'm aware of the criticisms and would simply come back and say there's other places where we were probably overly conservative in our accounting," he said. "We stand by the numbers."A commenter on Kos nicely paraphrases Mulvaney's position:
“These numbers are false. I stand by them. What? Snowflake, do you think there are facts?”Well, I used to.