In the Battle of Palo Alto, the first major engagement of the war, Taylor's troops forced Arista's from the field, suffering only four dead to hundreds for the Mexicans. The next day, Taylor led the army to victory in the Battle of Resaca de la Palma, putting the Mexican Army to rout.[165] The early successes boosted support for the war, which despite the lopsided votes in Congress had deeply divided the nation.[166] Many Northern Whigs opposed the war, as did others; they felt Polk had used patriotism to manipulate the nation into fighting a war the goal of which was to give slavery room to expand.[167]
Polk distrusted the two senior officers, Major General Winfield Scott and Taylor, as both were Whigs, and would have replaced them with Democrats, but felt Congress would not approve it. He offered Scott the position of top commander in the war, which the general accepted. Polk and Scott already knew and disliked each other: the President made the appointment despite the fact that Scott had sought his party's presidential nomination for the 1840 election.