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.

WASHINGTON—Several of Republicans’ largest proposed spending cuts can’t be done as written in the fast-track budget process they are using to advance their megabill, the Senate parliamentarian determined,