Perhaps you can answer this question. The closing sentence in the dialogue reported to have taken place with Lincoln is, "What then would become of my tariff?"
Since President Buchanan signed the bill on March 2, 1861, he might have described the Morrill Act as "his tariff". But how could Abraham Lincoln claim ownership, even figuratively?
Lincoln certainly supported the bill and always campaigned on standard Whig principles such as a high protective tariff. The Senate passed the Morrill Act after Lincoln's election but before his inauguration. The House of Representatives had passed the bill in May 1860. In what sense could Lincoln claim ownership of the actions of a Congress that adjourned before he became President?
In what sense could any President claim ownership of a bill passed by a prior Congress?