Democrat Hillary Clinton aims to build an impregnable lead on "Super Tuesday", the most consequential day of the presidential nominations calendar, while Republicans struggle to derail their insurgent and controversial front-runner Donald Trump.

With barely 24 hours before the big day, Clinton and Trump are well positioned to secure the lion's share of the delegate bonanza in the 11 states voting in each party's primaries.

Clinton, riding high after thrashing rival Bernie Sanders on Saturday in South Carolina, could come close to staking her claim to the nomination on Tuesday when the race goes national, after a string of smaller but important single-state contests.