Super Tuesday could prove decisive for Donald Trump and Hillary Clinton in race for nomination

Far from hitting a plateau, Mr Trump's support appears to be only increasing, despite the pounding he took in last week’s candidates’ debate

Hillary Clinton speaks during a "Get Out The Vote" event in Boston, Massachusetts, as she campaigns ahead of Super Tuesday (Getty)

Super Tuesday, when a dozen states vote, is the biggest day of the primary season, with the largest single haul of convention delegates at stake. On this day the process of electing a president goes national. And this year it could effectively resolve both parties’ nomination battles.

A sweep or near-sweep by Donald Trump would make it close to impossible for any Republican rival to overtake him, barring a colossal bolt from the political blue. Much the same goes for Hillary Clinton in her straight fight with Bernie Sanders.

Eight southern states are among those voting. If her substantial victory in South Carolina on Saturday is a guide, Ms Clinton’s overwhelming support among black Americans could propel her to victory in every one of those states, including Texas, the biggest prize at stake (and where, on the Republican side, home state Senator Ted Cruz must hold Mr Trump at bay by winning, to keep his candidacy alive.)

If that happens, and given Ms Clinton’s near monopoly of her party’s 700 non-elected “super-delegates” at July’s Democratic convention in Philadelphia, she will be well on the way to the 2,383 total she needs for victory. Mr Sander’s path to the nomination, even if he does well in non-Southern states voting now – Colorado, Minnesota, Massachusetts and his home state of Vermont – will be all but non-existent.

A new national CNN poll confirms the Trump-Clinton ascendancy. Mr Trump has support from a stunning 49 per cent of Republicans, more than his four remaining rivals combined, and destroying any notion he has a ceiling of 35 per cent or so.

Far from hitting a plateau, his support appears to be only increasing, despite the pounding he took in last week’s candidates’ debate and the swingeing attacks by Marco Rubio, the Florida Senator on whom the shell-shocked Republican establishment is pinning its dwindling hopes of blocking Mr Trump.

Ms Clinton meanwhile leads Mr Sanders by 55 per cent to 38 per cent nationwide, upping her advantage since the previous such poll in late January, before primary voting began. Women, older voters, African-Americans and moderates side heavily with her, while young, independent and liberal voters are almost equally divided between the two.

Mr Sanders says he will fight on, whatever happens today. But on the Republican side, former neurosurgeon Ben Carson is likely to drop out, barring an unexpected surge in his vote. Mr Cruz might follow him if he loses in Texas; meanwhile Ohio governor John Kasich faces pressure from party elders to withdraw, to clear the way for Mr Rubio. That pressure will only grow if, as expected, Mr Kasich loses across the board today.