On the political drama House Of Cards, Kevin Spacey plays a United States president who will sink to any depths for power. But as the show tries to create high drama for its new season, the actor ruefully remarks that the real White House "is not making it easy for us" with its own antics.

"When we get together every season with our team of writers, we're determined to try to create as much drama as we can and to invent situations that convince our audience that the impossible can become possible," says the 57-year-old two-time Oscar winner (The Usual Suspects, 1995, and American Beauty, 1999).

But "some days, it's hard to tell who's a real politician and who's just playing one on television", he tells The Straits Times during a press visit to the set late last year.

Sitting beside him, co-star Robin Wright - who plays Claire, Frank Underwood's ambitious wife and Lady Macbeth - laughs. "They've taken all our good ideas," says the 51-year-old star of Forrest Gump (1994) and The Princess Bride (1987).

And she may be only half-joking. As the show returns for a fifth season on Netflix on May 30 - its first since the election of US President Donald Trump - it, like comedy cousin Veep (2012 to now), has to contend with a new political reality that is occasionally stranger than fiction.

Spacey says: "We have a 'crazy meter' of what we believe we can get away with on the show. That definitely seems to be widening."

For a series that uses verisimilitude to anchor its over-the-top Machiavellian scenarios, not overshooting that meter is critical.

House Of Cards' commitment to plausibility is apparent in a cavernous warehouse in Joppa, Maryland, where most of its interior scenes are shot.

A 11/2-hour drive from Washington, DC, these sets recreate the literal corridors of power, with scale versions of everything from the Oval Office to Air Force One, many almost identical to the real thing, right down to the mouldings and fabric.

But Spacey cautions that despite this, the show - which broke ground when it debuted in 2013, becoming the first prestige drama on a streaming service and the first to be widely binge-watched - is not trying to document American politics. "We're a drama, so I don't spend too much time comparing real-world politics to ours."

And the star promises there is still plenty for fans to sink their teeth into as the show continues to chart the Underwoods' extraordinary political ascent, which Frank once secured by shoving a reporter in front of a train.

"I hope the show is more than about politics. It's about human beings and their relationships and the complexities of those. And you could set this story in any number of corporations that are high-profile and that are driven by passion, ideology and money, and you would probably see people behave in not dissimilar ways."

The linchpin in this human drama is the unconventional bond between Frank and Claire, whose politically expedient marriage invites comparisons with power couples such as former president and first lady Bill and Hillary Clinton.

But Claire's political ambitions have increasingly clashed with her husband's, jeopardising the seemingly iron-clad alliance.

Spacey says the power dynamic between the Underwoods "is constantly shifting" and "nothing is set in stone", especially now that Frank is in the White House and Claire has her own power base.

"It was interesting, in the first season, watching two figures who were enormously close and determined, working in the way they did best - in the shadows. And then they had to try to work in the hottest, brightest spotlight you could be under, which affected their ability to manoeuvre."

Asked if the pair still love each other, the actor, who is unmarried, says: "Absolutely."

Wright - who has two children, aged 23 and 26, with ex-husband and actor Sean Penn, 56 - demurs. "I don't think they even know what that means any more."

But, Spacey argues, "you could probably ask that same question about anybody who's been married a long time".

"Things change relationships - where you live, the job you have, whether you have kids or don't. There are lots of things that complicate what may have started as something incredibly pure and beautiful."

The star notes that people are quick to judge when couples stay together in less-than-ideal circumstances, as the Underwoods do. "If people choose to stay together despite all the evidence they should actually break up, we often find ourselves questioning that because it makes no sense to our logic.

"But if you weren't there, you don't get it. You'll never know what building that trust - that no matter what, we will stay together - means. And there's something to admire about it."

•Season 5 of House Of Cards will be released on Netflix on May 30.