Lynne Sandford’s son Michael, 20, will be sentenced in the US on Tuesday after he admitted trying to snatch the officer’s weapon during a rally for Mr Trump in Las Vegas in June.
Sandford, who has autism, allegedly told officers after his arrest that his plan was to shoot the tycoon.
Mrs Sandford, who will travel to Las Vegas for the sentencing hearing, said her son fears Mr Trump may “choose to make an example of him” as she appealed for his return to the UK to receive psychiatric help.
She told the Press Association: “I’m apprehensive and nervous not knowing what the sentence might be.
“Michael is terrified. He phoned me 15 times through the night with severe anxiety over what the judge is going to say to him and the sentence he will be given.
“Although he signed a plea agreement, which should mean he receives between 18 and 24 months, the judge is able to overrule that.”
She added: “Michael is afraid that because Donald Trump is now president-elect, it may have some bearing on the judge’s sentencing.”
Sandford, of Dorking, Surrey, pleaded guilty in September to charges of being an illegal alien in possession of a firearm and disrupting an official function.
His mother said she has written to Prime Minister Theresa May and US President Barack Obama to ask for their help in securing his return to the UK to serve his sentence and receive psychiatric treatment.
“If there is anything they can do to help Michael before Donald Trump takes office, I urge them to do so,” she said.
She added: “Michael is remorseful over what he did. He fears Donald Trump may intervene and choose to make an example of him.
“Michael has been on suicide watch for a considerable amount of time. His weight fell below 8st, which is very low for his height.”
Mrs Sandford will travel to Las Vegas with her mother Christine and four-year-old daughter Jessica. Sandford’s father Paul Davey is also expected to attend.
The family has launched a crowd-funding campaign to raise £10,000 to pay legal costs in their fight to bring Sandford back to the UK to serve his sentence.
Donations can be made at www.crowdjustice.org/michael-sandford.