Barring the participation of larger military countries such as China and Russia, Iran (and the Middle East in general) does not have the capability to retaliate against the US in any militarily significant way outside of symbolic attacks on US bases in the area. Troops are never going to set foot on US soil. Planes are never going to reach US airspace. Missiles will be shot down over the water long before they get close to US territory. The US is in a unique position on the globe that makes any kind of military attack or invasion borderline impossible. I do not fear "WW3" or anything because Iran has no capability of taking action that could spark WW3 independently, or even in a coalition with regional allies.
What I do believe will happen will be terror attacks on the US mainland by suicide bombers and Iran sympathizers. It's the only possible way that Iran can directly attack the US in any meaningful way, as it would be again borderline impossible to stop a lone wolf attacker from landing on US soil, heading to Home Depot to buy some supplies, and pulling a Timothy McVeigh. And Iran isn't on a time schedule here. They can wait a month, 3 months, a year or more if they want, wait for our guard to be down, and launch a retaliatory terror attack in the middle of East Bumfuck, Idaho. Or smack dab in the middle of Chicago. Or at a baseball game. I am infinitely more afraid of them pulling something like that than I am of this turning into WW3.
And if Iran's top advisors have half a brain, they'll allow the US to continue thinking that today's attack on the base in Qatar is the end of it. The "symbolic gesture" of retaliation meant to save face. Let the US think that this is all they're going to do and then spend the next 6 months planning for the real attacks. Heck, play into Trump's ego and let him believe that Iran is too afraid of Trump to do anything else. He'd be dumb enough to fall for it.