Checks across the three branches
The US Congress (Senate and House) makes laws and controls the purse. The Senate confirms judges, cabinet officials, and senior appointees; the House can impeach officials. The President executes laws and can veto Congress; Congress can override a veto with a two-thirds majority. The judiciary interprets laws and can strike down laws as unconstitutional; the President appoints judges (with Senate confirmation), and Congress can impeach judges.
These overlapping powers create mutual dependence. Congress cannot fund initiatives the President opposes unless it overrides a veto. The President cannot implement policy without congressional appropriation. The judiciary cannot enforce rights without the other branches complying with court orders. This interdependence forces negotiation and prevents any single branch from acting unilaterally on major issues.
Constraints and their evolution
Original checks have evolved. The Senate's confirmation power has become more contentious as judicial and cabinet appointments have grown partisan. Executive orders have expanded from narrowly implementing statutory authority to broader policy-setting, stretching presidential power. Congress has delegated vast rulemaking authority to agencies (staffed by the President), effective executive legislating without congressional vote.
Recent decades show the system under strain when branches directly oppose each other: government shutdowns when President and Congress deadlock on spending, standoffs on appointments when the Senate refuses to vote on nominees, constitutional crises when the President refuses to comply with court orders. These tensions reflect deeper partisan polarization rather than flaws in the structure, but they expose how dependent the system is on norms of cooperation the Constitution cannot force.