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"NEVER, EVER THREATEN THE UNITED STATES AGAIN OR YOU WILL SUFFER CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE. WE ARE NO LONGER A COUNTRY THAT WILL STAND FOR YOUR DEMENTED WORDS OF VIOLENCE & DEATH. BE CAUTIOUS!" he tweeted in all capital letters on July 2018.
Just last month, he vowed, "If Iran wants to fight, that will be the official end of Iran. Never threaten the United States again!"
But after Iranian forces shot down an American surveillance drone in the early morning hours Thursday, Trump was prepared to retaliate with U.S. strikes on three different sites that could have killed 150 people, according to the president. Instead, he stood down.
While many in Washington breathed a sigh of relief, and Trump may still respond yet, some analysts cautioned that not acting at all would send a dangerous signal to the world -- that Trump, who was elected on campaign that called for an end to expensive wars in the Middle East, was not willing to take military action if the cost was too high. Instead, his use of "empty threats" did "damage American credibility," according to Kori Schake, deputy director-general of the International Institute for Strategic Studies.
"There's going to be a school of thought that says that we backed down, we've lost deterrence, and that this will only invite additional aggression from Iran, that they'll continue to push until we push back," said Jonathan Schanzer, senior vice president for research at the Foundation for Defense of Democracies. "Certainly, there are those in the region who are going to articulate that position and so-called hawks in Washington."
Trump's predecessor faced similar criticism in 2013.
"A red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized. That would change my calculus. That would change my equation," Obama said in August 2012. When confronted with that reality one year later, when Bashar al Assad's regime used sarin gas to kill hundreds in Ghouta, Syria, Obama ultimately did not strike. Critics, including some of Trump's closest advisers and allies in Congress, said it damaged America's credibility.
That was one of the motivations behind Trump twice ordering strikes on Assad regime targets after similar uses of sarin nerve gas in April 2017 and April 2018.
But to publicly downplay Iran's aggression when it downed the U.S. drone and then back off military strikes after ordering them "actually done much worse than Obama did with his 'red line' comment," according to Schake, who argued in The Atlantic that it's part of a dangerous pattern with Trump, whose administration "keeps constructing policies that require the use of military force to achieve objectives, when the president has repeatedly made clear he's unwilling to take that step. The administration points a gun, but won't pull the trigger, and that will encourage other adversaries to challenge America in other theaters."
Critics also say that it's Trump himself who makes a tense situation worse by creating "maximum pressure" campaigns that allow for few alternatives, such as the "fire and fury" threats against "Little Rocket Man" Kim Jong Un of North Korea.
"We have a president who basically runs the same play over and over again, which is he lights everything on fire and then he pretends to put the fire out and claim credit for it," said Colin Kahl, a top national security adviser to President Barack Obama and his Vice President Joe Biden.
Supporters, however, say Trump has strengthened his hand by backing down because he is backing up his claims that he is not seeking war, but diplomacy.
"The U.S. is buying a modicum of credibility here ... The U.S. appears to be sticking to its policy of economic and political pressure and has at least for the moment forestalled a direct response," said Schanzer.
That doesn't mean tensions have lowered, however, and some critics argue that now, given the confusion over what Trump's red line is and what his response would be, the risks of a wider conflict are even higher.
"These questions of what will and won't prompt certain types of responses, this type of uncertainty when the two countries are so close to a military confrontation is incredibly dangerous," said Kahl.