What did James Buchanan do that was unconstitutional?

James Buchanan, the 15th President of the United States, is often criticized for his handling of the secession crisis leading up to the Civil War. Many argue that his decision to uphold the Constitution by refusing to coerce Southern states back into the Union was unconstitutional, as it allowed states to secede without consequence. Additionally, his inaction and failure to address the spread of slavery and sectional tensions are seen as a neglect of his constitutional duty to preserve the Union. This passivity contributed to the escalation of conflict, raising questions about his adherence to the Constitution's intent.