Who has the power to confirm or reject presidential appointments in the United States?

The authority to confirm or reject presidential appointments in the United States lies specifically with the Senate. This power is established in the U.S. Constitution, which requires the president to seek the Senate's advice and consent for certain appointments, including federal judges, ambassadors, and other key government officials. The Senate holds hearings, conducts investigations, and votes on whether to confirm these appointments, thereby ensuring a system of checks and balances within the federal government. This process underscores the Senate's critical role in the legislative branch by maintaining oversight over the executive branch's personnel decisions.