Here is a senator speaking against the war:

Never was so momenteous a measure adopted, with so much precipitancy; so little thought; or forced through by such objectionable means.

On the passage of the act recognizing the war, I said to many of my friends, that a deed had been done from which the country would not be able to recover for a long time, if ever.

These deep impressions were made upon my mind, because I saw from the circumstance under which the war was made, a total departure from that course of policy which had governed the country from the commencement of our Government until that time; and this, too, under circumstances calculated to lead to most disastrous consequences.

We begin now to find the misfortune of entering into war without a declaration of war—without a declaration setting forth to the people the causes of the war, and one upon which they may hold the Government responsible.

I should have said that here was a senator speaking against the Mexican war. That was Senator John C. Calhoun in 1846 and 1847.