Homeland (Channel 4, Sunday, 9pm) is the kind of programme Mitt Romney would hate and Barack Obama would love.

It's complex and nuanced. It tackles the issue of terrorism but never offers simple solutions. It has characters tortured by the question: do we really know who we are? And it shows what fear can do. It can mess up a country. It can mess up a brain.

It also has Claire Danes, who continues to deliver one of the most remarkable performances of modern television: subtle, sympathetic, scary. Her character, Carrie Mathison, believes America is about to be attacked by terrorists, that there are enemies within, that nobody can be trusted. In other words, she's the perfect heroine for the modern, frightened America.

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At the start of the second series, we found Mathison struggling to move on from her shattered career in the CIA, most of which she spent trying to expose former US hostage Nicholas Brody (Damian Lewis) as a traitor. Meanwhile, Brody, who has secretly converted to Islam, has climbed another few rungs of US society and is now a prospective candidate for the vice-presidency. It might seem far-fetched that a man running for one of the highest offices in America is keeping the fact that he is a Muslim hidden. And then you remember that certain extreme Republicans still believe Obama is Muslim. The point is that, for them, the far-fetched has come closer to being the truth.

The other point of Homeland – perhaps its most powerful – is that the word terrorism has no meaning. In one of the most critical scenes in the first episode, Brody is approached by an Islamist agent posing as a journalist. She asks him to steal a list of potential terror targets and at first he is appalled. He will not be part of terrorism, he says. But it's not terrorism, says the agent, this is a justifiable act of retaliation; it is a state acting in self-defence. It's the rhetoric of America and the UK in the mouths of the enemies, and it's not easy to listen to. Which is a good thing: quality drama should make us squirm.

The other good thing is that none of this nuance, none of the subtlety that runs down and down through every layer of the script and the performances ever spoils the pacing, which is sharp and fast and frightening. The exhilarating scenes in which Mathison is chased through a market in Beirut are shot as a rebooted, digital-age Alfred Hitchcock would have done them: beautifully tense, exquisitely subtle, obsessively detailed. They certainly deal with the theme Hitchcock loved more than any other: what it feels like to be running away.

And just look at Danes's face in those scenes. Look at how all the strain inside shows right through the epidermis, how it reflects everything that's going on in her head: the fragility, the fear, the mental illness. It's a triumph of modern realist acting even though it's sometimes not easy to watch. But you should watch it, and so should Barack Obama and Mitt Romney, because that face of a CIA agent being hunted through the streets of Beirut is the face of the modern West and the new America: confused, drugged-up, fearful.