Hillary Clinton has opted out of a keynote speaking engagement in favour of making fun of Donald Trump on a US comedy show.
US Vice President Joe Biden has also had a dig at his rival presidential nominees, even though he hasn't announced whether he's joining the race.
Mr Biden is expected to announce in the coming days whether he'll run for US president. But during a speech to a gay rights group, he took a pre-emptive cheap shot at his potential opponents.
As Republican presidential candidates are being urged to trim the field, Mr Trump has revealed there's only one way he'd abandon the race, and that's if his polls decline. He told NBC he's "not a masochist".
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