Nurse an Omnibus
(To) is to try and run it off the road. This is done by sending a rival omnibus close at its heels, or, if necessary, one before and one behind it, to pick up the passengers. As a nurse follows a child about regardless of its caprices, so these four-wheel nurses follow their rival.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894