Why has there been an increase in the President of the United States' exercise of the 'Commander-in-Cheif' role?

The Presidency of the United States is one bound by constitutional checks and balances as set out by the Founding Fathers to prevent a tyrannical President. The formal constitutional constraints on the President in the domestic realm – whereby he or she is checked and constrained by the legislative and judicial branches of Congress and the Supreme Court, has led to an increase in the number of informal Presidential roles in the foreign policy realm, where there is more freedom to make standalone decisions. The recent history of the US Presidency suggests that Presidents who are willing to take full command of their constitutional role as ‘Commander-in-Chief’ are more likely to gain favourable public opinion, as was the case with President George W. Bush in his promise to wage a ‘war on terror’ following the events of 9/11. In addition to this, an ‘imperial presidency’ (as coined by Schlesinger), in which a President favours a dominant foreign policy, allows the leader of the executive branch to bypass the constraint of Congress in his/her decision-making.