Nixon betrayed US peace plans to end the Vietnam war, promising better terms to South Vietnamese President Thieu. This occurred before Nixon was President, making it not only a violation of law but treasonous. Nixon later forced Thieu to take the same deal. The war raged for almost another decade, killing tens of thousands of Americans, hundreds of thousands of Vietnamese, and costing hundreds of billions of dollars.
Nixon, along with unindicted co-conspirator and war criminal Henry Kissinger, secretly and illegally expanded the war into Cambodia and Laos, causing the deaths of tens of thousands, destabilizing Cambodia, and leading directly to the horrors of the ‘killing fields’ of Khmer Rouge.
Reagan re-started the cancelled B1 bomber program, costing a cool $100 billion. The bomber was never needed in war, having been supplanted by the stealth B2 bomber, but it helped the arms industry of Reagan’s home state of California. Reagan also imagined a missile defense system that was developed at a cost of billions but still, even after decades and hundreds of billions of dollars, certainly isn’t reliable and may not work at all.
Reagan sent Marines into Lebanon with no mission. They soon were withdrawn, but not before hundreds were killed in a bombing of their barracks. Reagan was the anti-Teddy Roosevelt: teaching terrorists in the middle east that Americans “talk loudly and carry a limp stick”. This fiasco cost mere hundreds of millions of dollars but also the lives of more hostages and hundreds of Marines.
Reagan encouraged a Marine Colonel to break laws prohibiting arms trafficking to the Contras of Nicaragua. This lowly White House staffer arranged secret sales of missiles and warplane parts to Iran, breaking our own embargo. The sales were intended to curry favor with the Mullahs, but no hostages were released and, predictably, new ones were taken. Money from sales (minus fees) secretly bought arms for the Contras, who were essentially right-wing terrorists opposing the democratically-elected Nicaraguan government. Providing arms was explicitly prohibited by Congress. The cost of this “neat idea” in lives and dollars were relatively light but our reputation as a democracy functioning under rule of law, not subject to the whims of a petty politico-military clique, was tarnished.
Bush (the elder), as VP under Reagan, was responsible for overseeing the arms-for-hostages-and-Contras deal. He could never remember what meetings he attended or what was discussed or decided. He apparently misunderstood his ‘oversight’ responsibility, thinking it was advice to overlook, instead of to stop, malfeasance and illegality.
Bush sent the armed forces to capture Manuel Noriega, a former ally and CIA source. Seems his buddy had gotten a little greedy in profiting from drug trafficking and was named in a US court. Hundreds of Panamanians were killed. It would've been so much easier to just invite his buddy up for a drink and arrest him.
Bush was ‘surprised’ when erstwhile buddy Saddam Hussein invaded Kuwait, though his ambassador, forewarned, had said "we have no opinion on the Arab-Arab conflicts, like your border disagreement with Kuwait". Bush, goaded by Thatcher to ‘man up’, formed a coalition of the ‘willing and the billing’ to recapture Kuwait. Then he encouraged opponents to rise up in revolt against Hussein. When they did, Bush declined to risk the coalition and allowed Hussein to use his aircraft and tanks to crush the rebellions. This debacle cost the lives of thousands, hundreds of billions of dollars, and further eroded our reputation.
Bush (junior) ignored explicit warnings that terrorists sought to fly ‘airplanes into buildings’. On 9/11, terrorists did exactly that. Bush went AWOL (again), flying off on Air Force One, leaving VP Cheney to start wars in Afghanistan and Iraq. Bush, Cheney and the Defense Secretary Rumsfeld all dodged the draft during Vietnam but were eager to send the army overseas in a ‘permanent war’ against terror and terrorists, with unclear or unobtainable goals. Soon, employing torture (enhanced interrogation), kidnapping (rendition), and imprisonment without trial (Gitmo), we had become what we professed to fight.
Bush and Cheney lied about Saddam Hussein's weapons of mass destruction and about his links with Osama bin Laden. Their contrived war against Iraq cost thousands of American lives, tens of thousands of Iraqi lives, and hundreds of billions of dollars.
Trump, another draft dodger, seems also eager for war with persistent tough talk and saber-rattling. “Conventional” war is not good enough, not big enough for this dotard, he wants to go toe-to-toe, nuclear conflict, with whomever (except the Russians who are so helpful with cash and probably not the Chinese who produce Trump stuff)…but North Korean, Iran…
You could look it up.