Firstly, anyone who has already bailed out on this series: shame on you. OK, so it’s no longer as sharp and nuanced as when Aaron Sorkin was penning every episode but, for all the changes and influx of new characters, The West Wing remains compulsively top notch.

We’re in season seven now. Who thought we’d all live so long? The annoying Mandy is a distant memory. CJ is now chief of staff. Leo is running for the VP’s job. Toby is facing jail for blabbing on matters of national security. Josh is a presidential campaign manager. Charlie has grown a beard.

If all this seems preposterous, consider the pace of change in politics itself. For instance, one minute you’re deputy prime minister with a huge department and salary, the next you’re deputy prime minister with a huge salary.

Season seven, to be the last, follows the campaign to replace President Bartlet, still played with great wit and humanity by Martin Sheen, though his appearances are all too infrequent.

The sides are clearly defined. For the Democrats, Matthew Santos, portrayed with Clintonesque zeal by Jimmy Smits; for the Republicans, Arnie Vinnick, as played by the always impressive Alan Alda. The show’s producers took the idea of a rivalry so seriously they staged a live debate between the two characters, not their best idea, it has to be said.

The West Wing has always been a left-leaning liberal utopian wet dream of what politics and public service would be like if the good guys and gals were in charge. Thus, the Democrats are who we are invited to cheer for. Even so, the often venal nature of political campaigning is laid bare: the stunts, the spin, the endless polling.

This week’s episode was poignant as its main story focused on Leo McGarry, the former White House chief of staff, struggling in prep for the VP debate. Leo, an ever present since the pilot, was played by John Spencer, who died last year.

He was a fine actor and a key component on the show’s success, portraying a character with fierce talent, strong belief and deep flaws, evidenced through addictions to alcohol and pills.

The other side of season seven is the last days of the Bartlet administration. There can never be enough CJ Cregg on screen, but there is less in this run than the previous six. Instead, the dreary, smug Will Bailey’s romance with the foxy national security advisor is allowed to take up too much time.

This is why many have turned their backs on The West Wing. If the show’s executive producer were a football manager they could be accused of playing their team out of position. The dignified, loyal Toby is revealed to be a snitch, albeit one who leaked for high moral reasons. Donna, the delightfully kooky assistant to Josh seems colder now, more political and less likeable as a result. Leo, who commanded total respect and had complete control when he was chief of staff, is at times out of his depth as running mate to Santos.

And yet, and yet … this is season seven. That means that by the end of the run there will have been 155 episodes. How many other drama series have lasted so long without having to evolve and adapt?

When Sorkin left, the quality dipped. Season five was the low point, but the race for the Democratic nomination in six re-energised the show and the presidential campaign is a logical way to end the Bartlet years.

This was a series that captured political life with humour, style and honesty. It debated the big issues and examined the tough choices those in power are faced with. It was a world away from the likes of Commander-in-Chief, the latest Washington drama to hit our shores (if abc1 counts).

And so The West Wing recedes into television history. We’ve been through it all with them on the roller coaster ride through the corridors of power; the shooting, the MS revelations, Zoe’s kidnapping, the removal and reinstatement of the president, Donna getting blown up, Sam leaving, Mrs Landingham’s death and CJ doing the Jackal.

We’ll miss them when they’ve gone.

What’s next?