The Democratic presidential debate did what it is meant to do – reveal strengths and characters of the candidates

She, not Bernie Sanders, is overwhelmingly the second choice of Joe Biden supporters

Bernie Sanders and Hillary Clinton laugh during Tuesday night's debate (AP)

The Democratic presidential debate in Las Vegas on 13 October proved to be an advertisement for the genre. The contrast with the equivalent Republican events, replete with childish barbs, chest thumping and an almost surreal detachment from the real problems that confront America, could not have been greater. There are justified complaints that US presidential politics are excessively focused on personalities, at the expense of serious discussion of the issues. Not on this occasion.

The debate offered several lessons, and may well have changed the dynamic of the Democratic contest. Foremost it exposed the limits of Bernie Sanders, the self-proclaimed “Socialist” senator from Vermont. His eminently justified tirades against Wall Street, and the ever-widening inequalities that distort US society, have fuelled his rise in the polls and galvanised the white liberal wing of the party, especially the young. But insurrectionary populism has never won the White House. In that respect, he may be compared to Jeremy Corbyn. After 13 October, a Sanders presidency remains as hard to imagine as a Corbyn premiership.

A second lesson was that Martin O’Malley, the former Governor of Maryland who performed with increasing confidence as the debate went on, should be a strong contender as the next generation of Democratic leaders emerges. But not in 2016. The evening belonged to Hillary Clinton, who at last reminded the country why she began the campaign as the overwhelming favourite for her party’s nomination, and as the most likely 45th US president.

There have been growing difficulties for Ms Clinton in recent weeks. The handling of the row over her use of a private email server while Secretary of State has renewed old concerns about trustworthiness. Her shifting positions on the issues have only reinforced an impression that she stands for nothing – a calculating robot who trims every word to the prevailing political winds. On 13 October, however, she banished such doubts, at least for the moment.

Exuding competence and a command of the issues her rivals could not match, she looked every inch a battle-hardened president-in-waiting. She was poised and determined, humorous on occasion and dismissive when it suited. She deftly threaded the needle of being loyal to President Obama while making clear where she would differ from him. She managed to attack Mr Sanders, above all on gun control, without appearing nasty. His presence in the field may have tugged her to the left, but seems to have improved her as a candidate. If Mr Sanders is the revolutionary, she convincingly presented herself as a pragmatic agent of incremental change, who would build on what Mr Obama has started. Not least, the tiresome Clinton psychodramas were nowhere in evidence.

Her strong performance may bring another major benefit. All along, her biggest threat has not been Mr Sanders, but the possibility that the Vice-President Joe Biden might enter the race. As Ms Clinton seemed to falter, that possibility grew. Very soon Mr Biden must make up his mind, and after watching the debate he may conclude that, despite his popularity in the party, there is no longer political space for him to run. In that case, the former First Lady would be the beneficiary. She, not Mr Sanders, is overwhelmingly the second choice of Biden supporters. If the Vice-President officially declares himself a non-candidate, her lead is likely to grow. And if the debate proved anything, it is that she would thoroughly deserve it.