This has to do with how items to be reconciled in the proposed budget are scored from a spending perspective. Rs (Trump) wants to treat the tax cuts as already accounted for, which is a departure from past CBO scoring practice.
"There are reports indicating that Senate Republicans will simply ignore any ruling by the Parliamentarian that an extension of the 2017 Trump tax cuts has to be paid for. Instead, they are claiming that the Chair of the Budget Committee, Senator Linsay Graham, has the authority to set the budget rules for consideration of the budget reconciliation legislation, and that he can rule that the tax cuts are the current baseline and do not have to be paid for.
Democrats are loudly objecting to this ploy. But they may not be able to stop the Republicans from proceeding in this manner."