Following the attacks of Sept. 11, 2001, the American defense budget doubled within a decade, and new defense institutions were added to the federal government. With an ever-expanding United States defense, the next president could be considered the most powerful person ever.
Although the Constitution states that Congress is tasked with formally declaring war, the United States has not formally declared war since World War II. Presidents have generally accepted the responsibility when the United States goes to war.
President Bush received near universal support for War on Terror
In the weeks following the 9/11 attacks, 92 percent of Americans polled by the New York Times were in favor of using military action against al-Qaida and the Taliban.
Vowing vengeance both from the White House in an address on Sept. 11, 2001, and during a joint session of Congress nine days later, Bush garnered a historically high 90-percent approval rating, according to Gallup.
Following the attacks on the United States, Bush asked Congress to approve the Authorization for Use of Military Force Against Terrorists act (AUMF), which gave the president broad powers to fight terrorists. The bill passed by a 420-1 margin in the House, and a 98-0 ledger in the Senate.
"In 2001, there was this debate of exactly what extent the president will do with this much authority," said Robert Farley, professor of political science at the University of Kentucky. "There was this debate inside the Bush administration where some people like (Assistant Attorney General) John Yoo and (Vice President) Dick Cheney were saying that the presidency is unfettered at all. Besides impeachment, the president could do whatever he wanted in terms of interpreting treaties, in terms of prisoners, in terms of going to war."
With broad power handed to the executive branch to fight terrorists, Yoo crafted highly controversial policy regarding the waterboarding of terror suspects, and to legitimize the United States' efforts fighting terror under the Geneva Convention.
Unlike past declarations of war, the AUMF gave the president authorization to use the military to fight groups considered a threat to the homeland wherever and whenever. The law did not place any restrictions on methods for fighting terrorists, allowing the Bush administration to develop policies such as the enhanced interrogation methods, and to place prisoners of war in Guantanamo Bay without trial.
Congress' lack of interest in foreign affairs coupled with the need to give the president the ability to launch an immediate attack allowed the commander-in-chief absolute power with few checks.
Although President Barack Obama issued an executive order on Jan. 21, 2009 ? his second day in office ? to officially end the United States' practice of using waterboarding, it is possible the next president could override Obama's order. While Democratic nominee Hillary Clinton has come out against enhanced interrogation tactics, GOP standard-bearer Donald Trump has said he is fond of the tactic.
"I like it a lot. I don't think it's tough enough," Trump said at an Ohio rally in June.
When Obama delivered an address in May 2013 to discuss his administration's plan moving forward after the United States would leave Afghanistan after 2014, he said he wanted to engage Congress on amending the AUMF.
"The AUMF is now nearly twelve years old," Obama said in 2013. "The Afghan War is coming to an end. Core al-Qaida is a shell of its former self. Groups like (al-Qaida) must be dealt with, but in the years to come, not every collection of thugs that labels themselves ?al-Qaida' will pose a credible threat to the United States. Unless we discipline our thinking and our actions, we may be drawn into more wars we don't need to fight, or continue to grant presidents unbound powers more suited for traditional armed conflicts between nation states.
"So I look forward to engaging Congress and the American people in efforts to refine, and ultimately repeal, the AUMF's mandate. And I will not sign laws designed to expand this mandate further. Our systematic effort to dismantle terrorist organizations must continue. But this war, like all wars, must end. That's what history advises. That's what our democracy demands."
With Congress' inaction on the issue, the AUMF has remained untouched since 2001.
Congress gave the Bush administration a couple blank checks in terms of the authorization of use of military force in Afghanistan and then in Iraq (in 2003)," Farley said. "Those authorizations are so broadly worded that they allow the executive branch to do anything it wants with respect to fighting those wars.
"They don't have much in the ways of geographic limits, they don't have much in the way of on limits on means or different kind of weapons. The reason that we are still fighting in Libya and Iraq and so forth even though Saddam Hussein is long gone is based on using these laws that were passed."
Even though the United States is not currently fighting al-Qaida or the Taliban ? groups considered directly responsible for the Sept. 11, 2001 attacks ? the AUMF has been used to justify a long-term battle between the United States and the Islamic State group in Iraq and Syria.
While the AUMF gives the president plenty of authority, it also gives the commander-in-chief flexibility to follow terrorists across global borders. This flexibility could be considered useful going against an organization such as the Islamic State group, which spans multiple nations.
"We live in a different world, the same constitution exists, in that we have an old constitution, so that means it is vague enough so it can be interpreted in different ways to accommodate the needs and interest of society and government," political science professor and foreign policy expert Timothy White said.
The AUMF also accounts for groups that are not associated with official governments. For instance, the majority of the Sept. 11 attackers were from Saudi Arabia; a nation that the United States is allies with.
What this means is that many nations, even ones the United States is on good terms with, have citizens wanting to attack using small, rogue armies.
"There are groups across the world that could be classified a terrorist organization," White said. "There are terrorist groups in many countries, so to think that all threats of terror will be gone are just wrong. The logic behind why terrorists exist is because they are militarily weak and want to have some mechanism to express their anger and outrage or resentment and want to use terror."
Military strength does not make the US immune from terror
The United States' military is not just the most expensive force in the world; the US spends more on defense than the next seven nations combined, according to the Peter G. Peterson Foundation.
The United States spends 3.3 percent of the national GDP in defense, which is more than China, the United Kingdom and Japan, but less than Russia and Saudi Arabia.
Despite having such a large military, the United States is still prone to lone wolf attacks, such as incidents that took place at the Boston Marathon in 2013 and the Pulse Nightclub in Orlando in June.
It is an unusual military dominance in the world," White said. "It has not been seen really in earlier eras? This is in some ways an unusual situation. Americans are frustrated that we have all this military capability and all this power but we don't get our way.
"There is not an equal translation of military power to political influence on the world. That is probably because we live in a world where the military can't solve all of the problems of ethnic conflict in different parts of the world. Often the solution to these situations is domestic solutions, not something from an outside power like the United States."