The shortest route by which to move US forces deployed in Iraq to Afghanistan is - through Iran.
It would be a bloody fight, but one in which the relative merits of the army of the Islamic Republic of Iran would come face to face with the most technologically advanced military machines history has ever known.
There is no such thing as a “surgical strike”, there shall always be collateral damage. The good thing would be, almost all the collateral damage would be on THEIR territory, one of the better strategies for fighting any battle.
The other strategy is to win, quicker the better.
And who knows, the bulk of the Iranians may even welcome the liberation. But that is not the objective. Gaining swift transit from Iraq to Afghanistan was the original goal, and mission creep should be suppressed to the degree possible.
We should not be trying to invade and occupy a nation of 50 million people. That is beyond the capability of our force structure. If your idea is to declare war, then declare it and claim all the legal rights that go with a declared war. We would have the right to interdict commerce, confiscate assets, institute air and naval blockade. Irani insurance rates would go thru the stratosphere. Their trade would evaporate. their treasury empty. Air strikes could be made against their internal infrastructure, destroying transportation and disabling communications. These things are possible with a formal declaration.