Former US president Donald Trump has lost his latest bid for a new judge in his hush money case, as it heads toward a key ruling and potential sentencing next month.

Judge Juan M Merchan on Wednesday declined to step aside, rejecting the third such request from lawyers for the Republican presidential nominee.

All three times, they argued that Mr Merchan has a conflict of interest because of his daughter’s work as a political consultant for prominent Democrats and campaigns.

Among them was Vice President Kamala Harris’s 2020 presidential run.

A state court ethics panel said last year that Mr Merchan could continue on the case, saying that a relative’s independent political activities are not “a reasonable basis to question the judge’s impartiality”.

Mr Merchan has repeatedly said he is certain he can handle the case fairly and impartially.

But with Ms Harris now Mr Trump’s Democratic opponent in this year’s White House election, Trump lawyer Todd Blanche wrote to the judge last month that the defence’s concerns have become “even more concrete”.

Prosecutors called the claims “a vexatious and frivolous attempt to relitigate” the issue.