Such a policy could no longer prevail without a war.

The Southerners had no faith in the fair intentions of their opponents.

They worked themselves into the belief that The whole anti-slavery party was Abolitionist, and the whole anti-slavery agitation national disloyalty.

But the issue had been so shaped that the war could be fought for the purpose of preserving American national integrity; and that was the only issue on which a righteous war could be fought.
Thus the really decisive debates which preceded the Civil War were not those which took place in Congress over states-rights, but rather the discussion in Illinois between Lincoln and Douglas as to whether slavery was a local or a national issue.

The Congressional debates were on both sides merely a matter of legal special pleading for the purpose of justifying a preconceived decision.