He practically invented the mockumentary with This Is Spinal Tap. He feigned – with the help of Meg Ryan – the best screen orgasm ever in When Harry Met Sally. And he got Jack Nicholson and Tom Cruise to shout at each other in A Few Good Men. But Rob Reiner has no wish to retread old glories, not when there’s vital work to be done. “I’m 71 now,” he says, “and I just want to do things I want to do.”

This month sees the release of Shock & Awe, his second political drama in a row after LBJ, which starred Woody Harrelson as President Lyndon B Johnson. While that was set in the civil rights era, his latest – which again stars Harrelson and includes a turn from Reiner himself – is in 2003, in the run-up to the US invasion of Iraq, when news agency Knight Ridder were a lone dissenting journalistic voice in America during the search for weapons of mass destruction.

The Bronx-born Reiner had already lived through the Vietnam war; the Iraq invasion “made no sense to me”, he says. “I just couldn’t believe we were going to war twice based on lies in my lifetime … the rest of the world pretty much knew this was a really ill-advised foreign policy move. Probably in America, it was maybe the worst ever in our history.” Making a film about the lead-up to the Iraq war felt right. “Nobody had really made a movie about how we got there and why we were there.”

With America now under the shadow of the Trump administration, Reiner feels his film resonates with the present. “The press in America is under attack and is being called the enemy of the people and there are accusations of fake news. The mainstream press, which is trying to get to the truth right now in our country, is really having a hard time breaking through.” An ardent Democrat, Reiner may look genial – all bald, bearded and cuddly belly – but he doesn’t hold back.

“Right now we’ve got this battle of the soul of whether democracy survives – what is true and what is not true,” he says. “It’s very scary here in this country.” I wonder if he sees Trump’s time in the White House as worse than George W Bush presiding over the Iraq war. He pauses. “If we’re not able to slow Trump down and slow this drift towards autocracy then the ultimate result is going to be a lot worse – which is the destruction of western-style democracy.”

While Reiner is well aware that America has been divided for a long time, he admits he was taken aback when Trump arrived and “exacerbated” the racial tensions simmering in the country. “I knew it was there but I thought it was a fringe thing. I didn’t think it was 35 to 40 per cent of the country thinking in these terms … it feels like we’re in the last major battle of the civil war which divided our country completely.”

He compares the complacency that allowed Trump’s rise to that of Brexit and the British vote to leave the European Union. Does he feel Britain is in disarray? “I think Theresa May is trying to do what she can do. I think she’s stuck in a very horrible situation there. The people of Great Britain have called for getting out of the European Union, but at the same time, how do you make the deal? It’s an impossible situation.”

Taking a stand: Reiner is fighting for safer gun regulations in the US (Getty) (Getty Images)

For a director primarily known for humour – he is the son of comic legend Carl Reiner – he’s serious-minded when it comes to politics. He co-founded the American Foundation for Equal Rights, an advisory group for same-sex marriage. Now he’s taking on the all-powerful National Rifle Association, as he campaigns for tighter gun laws. “We’re the only country that has these violent outbursts every day. We’ve got to do something about it.”

Achieving it is another matter. Reiner believes it will be impossible to “re-litigate the Second Amendment” of the Constitution, which spells out the people’s right to bear arms. “I don’t think we’re able to just get rid of guns. That’s not going to happen. But you can make them safer and make them less likely to fall in the hands of someone who is going to use them badly. Unfortunately, we’re never going to be like Canada, Australia or Great Britain. It’s just never going to happen.”

Over a decade ago, Reiner came close to running for governor of California against Arnold Schwarzenegger. In The New York Times, it was billed as The Terminator versus Meathead, the latter a reference to the character Reiner played in 1970s TV show All in the Family. He was serious about it, discussing it with his wife Michele and their three kids Jake, Nick and Romy. “There are five of us, and I basically polled 40 per cent of my own family,” he laughs, “so I figured if I can’t carry my own family, I probably shouldn’t do it!”

These days, he uses Twitter as his mouthpiece, whether it’s urging people to vote in the upcoming mid-term elections or aiming daily barbs at Trump (“the most morally bankrupt person to ever occupy the Oval Office” he stated recently). He’s all too aware of the negative uses of a “weapon” like social media, from spreading fake news to online abuse. “I think now [Facebook founder] Mark Zuckerberg is in a very weird place; he has to figure out ‘What do I do with this social platform?’”

We move onto Harvey Weinstein. It’s fast approaching a year since allegations around the movie mogul abusing his power for sexual gratification came to light. “First of all, I had no idea that Harvey Weinstein was doing any of this stuff,” he says. “I knew he was a bad guy and tough to deal with creatively for filmmakers, but I never knew he was doing these kinds of things to women. All of a sudden everyone is getting outed and it’s good; the MeToo movement … it’s all very good.”

Again, Reiner sounds a note of caution amid the hysteria. “Jaywalking and murder…there are different punishments,” he says. In other words, the behaviour of Weinstein and Bill Cosby, the comedian accused of multiple sexual assaults, is at the other end of the spectrum to ex-US senator Al Franken, who resigned over comparatively minor indiscretions. “They’re all being swept up and punished the same way. I think you have to figure this stuff out in some kind of reasonable way.”

Speaking to Reiner, you’ll find it impossible not to talk about Spinal Tap, a film that kickstarted a wave of mockumentaries with its tale of a hapless metal band on the road. “We didn’t even think of it in those terms,” he says. “We just thought ‘We’re doing a satire of what happens on a rock’n’roll tour.’ So I guess it did create that.” Next year is the film’s 35th anniversary and he promises a Tap reunion at the Tribeca Film Festival. “We’ll all be there to talk about it.”

Reiner’s CV is flush full of films that merit the full-on reunion treatment – Stand by Me, The Princess Bride, The Sure Thing among them. But this late-career interest in political drama has changed his outlook. Right now he’s heading to television with two shows in development, including one about the Supreme Court, where audiences are potentially huge. Does he think about retiring? “If somebody lets me do stuff I’ll do it,” he shrugs. “And when they say ‘no’, then I’ll stop.”