Two of the great political parties in the West - the Republicans in the United States and Labour in the United Kingdom - are in a state of near collapse. That, in turn, threatens the health of democracy on both sides of the Atlantic.
The crises in the Republican and Labour parties are strikingly similar. In both cases, a leader has emerged from the fringes of politics and taken the party in a different and radical direction. The emergence of Mr Donald Trump and Mr Jeremy Corbyn threatens to destroy the electoral prospects of their two parties - and will sow division and ideological confusion long into the future.
Even if Mr Trump and Mr Corbyn never make it into the White House or 10 Downing Street, their ascendancy is also damaging to the wider political system. Well-functioning democracies need a credible opposition to hold the government to account. But in the UK and the US, that basic function is no longer being properly performed.
In Britain, the challenge of negotiating the UK's exit from the European Union (EU) cries out for an alert and responsible opposition. The government, led by Mrs Theresa May, has managed to acquire a reputation for competence, partly because Labour is such a shambles. Yet, although two months have elapsed since Britain voted to leave the EU, there is very little sign that the May government has any idea of how to handle the issue. Simply repeating "Brexit means Brexit" is no substitute for a strategy.
A competent opposition would, by now, be all over the May government. It would highlight the infighting among the ministers who are charged with negotiating Brexit. And it would hammer the Prime Minister for failing to articulate her priorities on crucial issues, such as the trade-offs between immigration and access to the EU's internal market.
But Mr Corbyn's Labour Party has failed to do any of this. This may be because Mr Corbyn is actually a secret supporter of Brexit. Or it may simply be incompetence. Either way, the Labour Party is failing in its duty.
The situation in the US is more dire. Mr Trump's idea of opposition is to seize upon any crackpot conspiracy theory circulating on the Internet or on talk radio. The Trump campaign is so obsessed with painting Mrs Hillary Clinton and the Democrats as "crooked" that it has failed to highlight real problems that have festered under the Obama administration. These include the unfolding disaster in Syria and the worry that the US economy is addicted to ultra-loose monetary policies. In a well-functioning democracy, these issues would be at the centre of the presidential election. As it is, they have been lost in an endless series of controversies generated by the Trump campaign.
The similarities between the Corbyn and Trump phenomena are disguised by the almost comic differences between the two politicians. Mr Corbyn primly insists that he "doesn't do" personal abuse; Mr Trump does almost nothing else. The Labour leader is most at home in his allotment garden; Mr Trump's natural environment is a penthouse suite. Mr Corbyn is on the far left. Mr Trump is on the far right. Mr Corbyn is an internationalist; Mr Trump is a nationalist.
But, despite these differences, the two leaders have quite a lot in common. Both are "anti-system" politicians. Both have seized control of their parties by mobilising new groups of activists and voters. The Trump and Corbyn activists despise their parties' old guard and often have an undercurrent of violence in their rhetoric.
Mr Corbyn and Mr Trump are also noted for their sympathy towards Mr Vladimir Putin's Russia - and their scepticism about Nato. The fringes of the Corbyn and the Trump movements also seem to be infected by anti-semitism, perhaps reflecting the traditional suspicion of the far left and the far right that "the system" is controlled by Jews.
The similarities between the two movements suggest that traditional right-left divisions may no longer be the best way of understanding Anglo-American politics. Instead, the new politics is turning into a confrontation between establish- ment and anti-system parties.
The same pattern can be observed in much of western Europe, with the rise of anti-system parties such as Italy's Five-Star movement, France's National Front, Spain's Podemos and the Alternative for Germany. Some of these are described as far-right and some as far-left. The characteristic they almost all share is a claim that the system is "rigged" and that ordinary people are being trampled by elites. In foreign policy, they tend to be pro-Russian.
Given the disasters of the Iraq war and the financial crisis, combined with a long stagnation in living standards, it is not surprising that voters in the US and Europe are seeking more radical alternatives. But the standard-bearers of the new radicalism in the US and the UK are leaders who are sadly bereft of constructive ideas, unless you regard protectionism and the destruction of Nato as the keys to the future.
Instead of introducing creative new ideas, Messrs Corbyn and Trump have merely succeeded in recycling some bad old ones: state control of the economy in the case of Mr Corbyn; and America-first isolationism in the case of Mr Trump.
These two individuals may never gain real power. But their rise to prominence is a sign of a real sickness in British and American democracy.