[Non-Sequitur]

It could have something to do with the fact that there was still an election up for grabs in November and that the push for a tariff could still be halted.

They could have killed it in the Senate regardless. Why the change?

[GOPcapitalist]

They could have killed it in the Senate regardless. Why the change?

Not necessarily. An evenly split senate can tilt one way or the other depending upon who is in the White House. Lincoln made it very clear he was willing to influence the direction of that tilt if necessary.