The Senate's rule enforcer dealt a major blow to Senate Republicans Thursday morning by ruling a key Medicaid provision in the megabill that advances President Donald Trump's legislative agenda is out of order.

The nonpartisan Senate official whose office determines if legislation fits within the rules of the chamber dealt Senate Republicans a blow on proposed changes to Medicaid.

The Senate parliamentarian has advised that a Medicaid provider tax overhaul central to President Donald Trump's tax cut and spending bill does not adhere to the chamber's procedural rules, delivering a crucial blow as Republicans rush to finish the package this week.