Threatening war is a violation of the U.N. Charter.
Waging war is a violation of the U.N. Charter and of the Kellogg-Briand Pact.
Waging war without Congress is a violation of the U.S. Constitution.
Have you seen Iraq lately?
Have you seen the entire region?
Have you seen Afghanistan? Libya? Syria? Yemen? Pakistan? Somalia?
War supporters said the U.S. urgently needed to attack Iran in 2007. It did not attack. The claims turned out to be lies. Even a National Intelligence Estimate in 2007 pushed back and admitted that Iran had no nuclear weapons program.
Having a nuclear weapons program is not a justification for war, legally, morally, or practically. The United States has nuclear weapons and no one would be justified in attacking the United States.
Dick and Liz Cheney's book, Exceptional, tell us we must see a "moral difference between an Iranian nuclear weapon and an American one." Must we, really? Either risks further proliferation, accidental use, use by a crazed leader, mass death and destruction, environmental disaster, retaliatory escalation, and apocalypse. One of those two nations has nuclear weapons, has used nuclear weapons, has provided the other with plans for nuclear weapons, has a policy of first-use of nuclear weapons, has leadership that sanctions the possession of nuclear weapons, and has frequently threated to use nuclear weapons. I don't think those facts would make a nuclear weapon in the hands of the other country the least bit moral, but also not the least bit more immoral. Let's focus on seeing an empirical difference between an Iranian nuclear weapon and an American one. One exists. The other doesn't.
If you're wondering, U.S. presidents who have made specific public or secret nuclear threats to other nations, that we know of, as documented in Daniel Ellsberg's The Doomsday Machine, have included Harry Truman, Dwight Eisenhower, Richard Nixon, George H.W. Bush, Bill Clinton, and Donald Trump, while others, including Barack Obama, have frequently said things like "All options are on the table" in relation to Iran or another country.
War supporters said the U.S. urgently needed to attack Iran in 2015. It did not attack. The claims turned out to be lies. Even the claims of supporters of the nuclear agreement reinforced the lie that Iran had a nuclear weapons program in need of containment. There is no evidence that Iran has ever had a nuclear weapons program.
The long history of the United States lying about Iranian nuclear weapons is chronicled by Gareth Porter's book Manufactured Crisis.
Proponents of war or steps toward war (sanctions was a step toward war on Iraq) may say we urgently need a war now, but they will have no argument for urgency, and their claims are thus far transparent lies.
The U.S. ambassador to the United Nations claims that Iranian weapons have been used in a war that the U.S.., Saudi Arabia, and allies are illegally and disastrously waging in Yemen. While that's a problem that should be corrected, it is hard to find a war anywhere on the planet without U.S. weapons in it. In fact, a report that made news the same day as the ambassador's claims, pointed to the long-known fact that many of the weapons used by ISIS had once belonged to the United States, many of them having been given by the U.S. to non-state fighters (aka terrorists) in Syria.
Fighting wars and arming others to fight wars/terrorism is a justification for indictment and prosecution, but not for war, legally, morally, or practically. The United States fights and arms wars, and no one would be justified in attacking the United States.