Former Maryland Gov. Ehrlich says Giuliani has “a lot of explaining to do” if NYPD ferried Nathan on taxpayer’s dime.

Update: After talking to campaign, Ehrlich goes back on the reservation.

Plus: Former NYC official calls Giuliani billing explanation “so disingenuous.”

Earlier: Nathan’s friends and family got NY police “taxi service” in 2001, even when she was not there. Campaign calls claims “absolutely ridiculous.”