The US Would Lose a War with Iran; On Many Levels
Going to actual war with Iran would be a huge mistake and the first real war the United States has fought since Vietnam.
Iraq, Afghanistan, and the last few wars over the past 50 years most people have never heard about were mismatched based on military size and technology. But Iran has a real military and many more soldiers.
Iran has a navy with a fleet of ships (something Afghanistan or Iraq did not have) and they have an air force with bombers, missiles, and an array of troops stationed around the Middle East. When the US launches bombers into the air, so will Iran; When the US fire off missiles toward them, so will they toward the US; and when the US drops boots on the ground, there will be just as many Iranian soldiers there to meet them.
But military might is not the reason the US would lose fighting Iran. Because Iran's military is much stronger, it will take the US much longer to defeat them which means spending more money and dispatching more resources and troops on a consistent bases. That also means less money being spent on the domestic front at home and the current problems the country has will only increase.
Unless someone has a job at a defense factory, wages will remain stagnant and social policy will not get passed as fast - if at all - because most attention of the politicians will be on the War. Forget about an infrastructure bill to create jobs, or Medicare for all, or free college; there will be no money for them in the near future. The war will drain the US budget dramatically.
Not only will the US lose economically, but they will lose internationally where it pertains to allies and enemies. Russia and China have a vested interest in the Middle Eastern region along with other countries, and who's to say they would not join in on behalf of Iran.
The European Union and NATO are not on good terms as they used to be with the US. The US has offended those and other allies and bullied them into false negotiations, bad trade deals, and have also broken or horribly renegotiated peace talks, deals, and treaties.
Furthermore, in the strategic level of war, if Iran begins to get the best of the US in terms of killing the troops and out maneuvering them on the battle fields and in the seas, the US will have to use more force because they will be humiliated on the world stage. This will definitely lead to the US considering using the nuclear option. If this happens, and they launch a nuclear missile toward Iran, that will mark the beginning of the end of civilization.
If the end game is to take over the country of Iran and implant another regime that will take American bribes, it may not work seeing it did not work in Iraq. The people of the US still have not seen the rewards of that take over. Plus, there is a chance that many more of the US soldiers will die in Iran than died in Iraq and many more will come home with PTSD, not to mention they will probably be there for the next 20 years like they are still in Iraq and Afghanistan.
This is a horrible idea yet the war hawks of the administration are pushing vehemently for war and trying to convince the people using the media to stand behind them. Remember, this is a Republican led effort, backed by this President and the wealthy warmongers greedy for oil, yet paid for by your hard earned dollars.
So regardless if the US kills more soldiers than Iran does them, or if they destroy more of Iran's military power, their cities and towns and even if they nuke the entire country, the world loses and the United States lose tremendously because they lose respect and trust of the rest of the world, and not to mention their own citizens if the war cost the people their livelihoods.