Final answer:
The Senate may not approve a cabinet appointment due to past behavior issues or controversies related to the nominee, or because of political obstruction and partisan disagreement.
Step-by-step explanation:
There are two major reasons why the Senate might not approve a president's cabinet appointment. First, a nominee may face issues related to past behavior or controversies, which raise questions about their suitability for the position. This was the case with Senator John Tower, whose issues involving alcohol and womanizing led to concerns about his fitness to head the military, and Zoe Baird, whose nomination was compromised by the hiring of undocumented workers, a scandal that became known as "Nannygate". Second, political obstruction and partisan disagreements can also lead to the rejection of a nominee, which has become increasingly common when there is a split between the political party of the President and the majority in the Senate.
Historically, the Senate has guarded its constitutional duty to consent to the President's nominees and typically confirms them. However, cabinet confirmations can be delayed or derailed by the Senate as part of political strategy or protest against the President's policies. In addition to individual concerns about nominees, the Senate might use their confirmation powers to scrutinize the President's nominees and leverage over the executive branch's appointments.