Definition of "Preempt" :

noun: a high bid that is intended to prevent the opposing players from bidding

verb: make a preemptive bid in the game of bridge

verb: acquire for oneself before others can do so

verb: gain possession of by prior right or opportunity, especially so as to obtain the right to buy (land)

verb: take the place of or have precedence over

"Live broadcast of the presidential debate preempts the regular news hour."