To be sure, Congress is the only branch of our central government that can legally declare war; but, for instance, other nations are not hampered by our Constitution, and might attack us in such a manner as to prevent Congress--for a time, at least--from acting. None the less we should fight, and it would be nonsense to describe our resistance as unconstitutional. As a matter of fact Congress did not declare war against Mexico, and on Calhoun's theory we had no lawful war with that country. On that theory, not only our military men, Congress and the President, but our Supreme Court, which fully recognized the war, acted unconstitutionally. Indeed, he himself illustrated the untenability of his idea. In order to avoid the weakness of advocating purely defensive operations a Whig leader, Senator Crittenden, said that by repelling invasion he meant pursuing the enemy until we could be sure that no repetition of the outrage would occur. This programme would have involved substantially all that we did against Mexico. It would have meant a war without a declaration; yet Calhoun endorsed it. In short, even one so acute and so deeply interested as he could not find a real argument against the war bill, and his "friends" abandoned him on this issue. By an overwhelming majority Congress rejected his interpretation of the organic law. War existed. No American who recognized our claim to the intermediate region, formally made by national authorities and never withdrawn, and especially none who recognized the claim of Texas, could logically deny that it existed by the act of Mexico; and in the light of its antecedents, including Arista's declaration of war and attack upon Thornton, the war bill committed the nation properly as well as completely.[9.10] [THE CAUSE OF THE WAR] We were, then, under arms; but, after all, why? What was the cause of the war? It was not--as will plainly appear in another chapter, it is believed--an unholy determination to obtain California at the cost, if necessary, of fifty thousand lives. It cannot have been a difficulty as to the boundary of Texas, for two nations do not fight over an issue that exists for only one of them--and that one not the aggressor; and for Mexico the question between the Nueces and the Rio Grande had no international significance except when it could be used, as an _argumentum ad hominem_, to embarrass Americans.[9.14]