That's what careful readers of the administration's budget must assume. After all, the budget tells us that we should expect savings of $59 billion in 2028 from reducing "improper payments Government-wide" (Table S-2). However, we build up to these large annual savings very gradually. There is nothing noted for savings in 2019 and just $1 billion in 2020. Even in 2024, the last year of a hypothetical second Trump administration, the projected savings are only $6 billion. 

If we assume that these improper payments were always there, but it will take vigilant effort and ten years to weed out the full $59 billion (and even in 2028 there could still be more improper payments) it means that we could be improperly spending more than $50 billion a year throughout the Trump administration. And that is their assessment.