The US has been pouring resources into developing countermeasures against nukes but current capabilities aren't enough to offer any meaningful protection.
The engineering problem has best been summed up as "trying to block a bullet, using another bullet." While ICBMs are 1970s technology, they take roughly 30 minutes to reach their target from launch. The Reentry Vehicles travel at hypersonic velocity and can very cheaply/easily be loaded with chaff (e.g. fucking metal plates cheap/easy) that give off similar radar signatures during the critical minutes that a Reentry Vehicle can be shot down. This problem is an order of magnitude more difficult to deal with than the drones that are currently giving Russian and Saudi AA hell.
The silver lining is that the Russian nuclear arsenal has been known for years to have shit reliability (e.g. they drive out to a silos to discover it's completely flooded - where as a water leak in a US silo will be discovered within a week as we take Nuclear Surety very seriously). In theory, they compensate for worse reliability and accuracy with higher warhead yields but judging from their performance in the Ukraine, a significant number of their reentry vehicles will fail to hit their targets.
That being said, we still need to take the threat seriously. A single High-Altitude Electromagnetic Pulse (e.g. a single Nuke detonated in the upper atmosphere) is enough to knock out the entire electrical grid of the United States. This sort of attack is virtually unstoppable.
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This means every bank account, stock exchange, crypo wallet, website, and any appliance plugged into the electrical grid gets immediately fried. We're talking trillions of dollars in damage if even one of their nukes gets off a national EMP. The only thing that's been preventing nuclear war for nearly a century is mutually assured destruction. Our nukes have massive Electoral Surge Arrestors that can withstand the pulse that will spread throughout the power grid and massive diesel generators and batteries that will give them enough power to give Russia the exact same treatment if they strike first.