The Republicans need a dose of Lincoln's human factor

Out of America: The party's swing even further to the right has prevented compromise in American politics

Political wiles: Daniel Day-Lewis as Lincoln, who could handle the opposition (Dreamworks)

Yes, it's fiscal cliff countdown time. Will the Republican-controlled House of Representatives and the White House strike a deal to avert the looming tax increases and budget cuts before tomorrow's deadline? Or is tomorrow really the deadline? And, despite the doom-mongering, does it really matter? Some eminent economists now argue it would be better if we do go over the cliff.

But the cliff-talk obscures the real story: how this impasse has been reached because the Republican Party, prisoner of its extreme conservative wing, for whom tax cutting is all, has simply gone off the rails. If you don't believe me, then consider Norman Ornstein and Thomas Mann, of the conservative American Enterprise Institute and the liberal-centrist Brookings Institution respectively, both of them dispassionate, experienced observers of the US political scene, about as unpartisan as you can get.

Yet, in their book earlier this year on the dysfunctional system that has spawned the fiscal cliff debacle, entitled It's Even Worse than It Looks, Mann and Ornstein let slip any pretence of even-handedness. "One of our two major parties, the Republicans," they write in exasperation, "has become an insurgent outlier – ideologically extreme, contemptuous of the inherited social and economic policy regime, scornful of compromise, unpersuaded by conventional understanding of facts, evidence and science, and dismissive of the legitimacy of its political opposition."

The Republicans, in short, have lurched so far to the right that politics in the normal sense of give and take, of taking other points of view into consideration, has become virtually impossible. Yes, Democrats must bear some of the blame for the stalemate, but only a small part. Their move to the left is far less than the Republican shift rightward.

Ronald Reagan is the saint to whom modern conservatives mouth ritual devotion. But Reagan, always ready to make a deal when he had to, would be lost amid today's Republican zealotry, where moderates have been systematically expelled and ideology is now all. But it was not always thus – as a couple of things reminded me last week.

The first was the turn for the worse in the health of George H W Bush, Reagan's Republican successor in the White House. Bush is now 88 and in intensive care, being treated for bronchitis. Happily, the last news was more encouraging: "Put the harps back in the closet," was his mood, according to a spokesman.

Bush is America's oldest living former president. More to the point, he's the sort of Republican you don't find any more, a patrician moderate and East Coast establishment gentleman, who might have been a bit out of touch on occasion, but whose heart was in the right place. Yet the elder Bush is anathema to great swathes of his party.

His sin was to have abandoned his celebrated 1988 campaign pledge of "Read my lips, no new taxes", when economic facts of life obliged him to strike a deficit reduction deal, two years later, with the Democrats who then controlled Congress. The deal helped to pave the way for the boom later in the decade, but it is an article of faith for modern Republicans that the broken pledge was responsible for his 1992 election defeat. Never again, they said – and so it has been.

The other reminder came from a Republican of the 19th century, whose occupancy of the White House prevented the country from sliding off an existential cliff, in comparison with which the 2012 fiscal variety is the gentlest incline.

Steven Spielberg's Lincoln is being released in the UK on 25 January, and don't miss it. Not only does Daniel Day-Lewis deliver an unforgettable portrayal of America's greatest president, as he seeks passage of the 13th amendment, banning slavery, through the House of Representatives in the final months of the civil war (and his own life). It is also perhaps the most realistic cinematic depiction ever of how the US political system, with its separation of powers, works.

Lincoln knows his opponents' foibles. He wheedles, flatters and cajoles; he appeals to their best instincts and, when necessary, their worst. On occasion, he stretches the truth almost to breaking point. And, in the end, he rounds up the votes required, without betraying his principles.

The message of the movie is not so much that compromise is essential in politics (although it is). Rather, it is that politics is ultimately about people and how humans interact with one another. Obviously, there is a lesson for President Obama as he seeks a way down from the cliff-edge. Wheedling and flattering is not his style; all too often, he seems contemptuous of the human spadework at which Lyndon Johnson excelled.

But the greater lesson, laying bare the terrible flaw of US politics as currently practised, is that this human factor has vanished from the Republican Party. When only ideological purity matters, everything else is pointless. Even LBJ wouldn't have had a prayer with the Tea Party.

Worst of all, the mess is of the Republicans' own making. They hold a 233-200 majority in the House, even though they lost the popular vote in congressional elections by over half a million. Americans, in other words, didn't vote for a Republican House in 2012. They got one however, thanks to the gerrymandering of Republican-controlled state legislatures.

But gerrymandering also makes seats vulnerable in primaries to intra-party challengers claiming greater ideological purity. Thus moderates are driven out and extremists take over. Now, however, the revolution is devouring its own. Before Christmas, the House Speaker, John Boehner, was humiliatingly forced to withdraw fiscal cliff legislation, as dozens of Republican members, arch-purists all, rebelled. A party that loses control of itself is surely doomed. America teeters on the fiscal cliff – but, for Republicans, the political cliff that looms is steeper still.