No democracy is without its autocratic features. In Britain, the Prime Minister gets to choose the date when the voters are allowed to re-elect him. In Russia, the President gets to come back as Prime Minister so he can go on running the country even after his constitutionally imposed term limits have expired. In America, the leadership of the world’s most powerful republic is constitutionally available only to members of two families.

Or that at least is how things seem now in Washington.

The stately procession of Hillary Rodham Clinton to the White House accelerated sharply this week. On Tuesday she announced that she had raised more money for her campaign this year than the two leading Republican hopefuls combined (“hopefuls” is a bit of a stretch – “laughably overmatched pretender” is probably better).

On Wednesday a couple of opinion polls suggest she now enjoys a lead of as much as 33 percentage points over Barack Obama, the nearest of her Democratic rivals for the nomination (“rivals” is a bit of a stretch – “supplicating retinue” is probably better). The same polls indicate she is being helped by the growing popularity of Bill Clinton, her husband (“husband” is a bit of stretch . . .)

And so Americans are starting to embrace the inevitability of the prospect of eight years of another President Clinton. Thus, after a previous Clinton Administration sandwiched between two Bushes, the strong likelihood is that, between 1988 and 2016, just two families will have supplied America’s president.

You have to go back to the Borgia-Medici rivalry to find parallels for such dynastic supremacy. There’s something alarmingly persuasive about the Clintons as the Borgias but the mind rebels slightly at the idea that the Bushes should be seen as the latterday Renaissance men of Florence.

But before we get completely carried away on the reverie of a post-republican America, we should review the current political wisdom about Mrs Clinton and ask: is she really inevitable?

The consensus in Washington is certainly that she is about as close to unstoppable for the Democratic nomination as any candidate has been in an openly contested race in living memory. She began her campaign nine months ago with powerful advantages – the name, a national political network in place that eclipsed the other candidates; money. Those were institutional advantages. What was not clear was whether she could complement them with real political skill. In the ensuing nine months she has removed any doubt. She has conducted a roughly flawless campaign so far.

It has been designed to address what would always be the biggest objection to a Hillary candidacy – could she win a national election? She might be admired and respected by Democrats, but could she overcome the almost rabid opposition she provoked in much of the country – the rancid legacy of the 1990s, with all those memories of dodgy property deals, assertively feminist conceptions of her role as First Lady and left-wing ideas about the role of government?

The makeover that began when she was elected to the Senate in 2000 has intensified this year. She has fought what has been in effect a general election campaign, appealing to moderate voters in the country, not principally to Democratic primary voters, thereby neutralising concerns about her electability.

She has done this especially over what has always been for Democrats the problematic issue of national security. She has declined to give in to demands from the Left that she apologise for her support for the Iraq war. She has sounded positively belligerent on Iran, last week earning the distinction of being the only leading Democratic contender to vote in the Senate for a resolution designating Iran’s Revolutionary Guard as terrorists.

So the arguments of her opponents, uttered with diminishing conviction, that she cannot be elected because she is too out of step with mainstream America, sound hollow. Democrats, for all their furious opposition to the Iraq war, are anxious not to scare the voters. They want someone who can win and Mrs Clinton is steadily convincing them she can.

So what – or who – can stop her? The dwindling band of Democrats who worry about or dislike Mrs Clinton continue to indulge the fantasy that Al Gore, once merely a failed presidential candidate, now the Saviour of the Planet, might come to their aid. His friends have always said his resentment of the Clintons burns so brightly that he would only run for the Democratic nomination if he thought it was the only way to stop Hillary. Next Friday he is expected to receive the Nobel Peace Prize for his climate change campaign. Might he pivot from Oslo to Ohio and make a dramatic late bid for the presidency?

Unlikely, say those who know him. If Mrs Clinton is to be defeated for the nomination, it will have to be by one of the current crop. And the only person who can do that is Mrs Clinton herself. Only some gigantic misstep between now and the primary votes early next year seems likely to stop her. Given how disciplined her campaign has been so far that seems highly unlikely.

But there is one caveat. Mrs Clinton has a vast advantage in the national polls, but that lead will matter less as we approach the first primary states. History suggests that victory in one of the early primary contests – Iowa and New Hampshire – can upset the national standings with remarkable speed.

It is Iowa, the very first state to vote in early January, where, as it happens, the Clinton campaign is weakest. She has never had a strong base there and polls indicate she is barely level with the other candidates – one this week even put her behind Mr Obama. A slip-up in a snowy Iowa winter is the one thing that could undo her.

The Clinton dynasty is almost – but not quite – assured. The Borgias, fortunately for Iowans, never had to carry Iowa.

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