San Diego's riot police broke up skirmishes between supporters and opponents of presumptive Republican presidential nominee Donald Trump on 27 May. Authorities fired pepper spray and made 35 arrests "due to violence and physical confrontation in the crowd", after protesters refused to disperse when the demonstration was declared illegal.

Police in the Californian city close to the Mexican border said the gathering was initially peaceful. At least 18 people required medical attention by its conclusion, according to reports.

Around 1,000 people reportedly turned out for anti-Trump rallies waving US and Mexican flags and bearing signs which read "F**k Trump." While the atmosphere inside the San Diego Convention Center was calm, tensions rose outside the venue as some protesters scaled a barrier and hurled water bottles at police. As the convention centre emptied, supporters from both camps mixed in the streets, taunting one another.

Trump took to Twitter to praise police handling of "the thugs who tried to disrupt our very peaceful and well attended rally".

But demonstrator Martha McPhail spoke out against the controversial billionaire businessman, whose campaign has been dogged by criticisms of racism after he called for a temporary ban on all Muslims entering the US and pledged to build a wall along the US-Mexican border at the latter's expense.

"I am opposed to the hateful, bigoted, racist language of Donald Trump and his arrogance and intolerance," McPhail told the local City News Service (CNS). "I'm for all of our people – all races, sexes, genders, military veterans – and he's divisive," she added.

But 19-year-old Trump supporter, Riley Hansen defended Trump, saying the US needs a leader with a business background. "My dad always told me you need a businessman as president," he told CNS. "I like his policies."

After days of flip-flopping, Trump ruled out taking on Democratic candidate Bernie Sanders in a one-on-one debate despite previously saying he would "love to debate" the Vermont Senator. The presumptive GOP nominee said it would be "inappropriate" and that he would only take on the winner in the Democratic race.

"As much as I want to debate Bernie Sanders – and it would be an easy payday – I will wait to debate the first place finisher in the Democratic Party, probably Crooked Hillary Clinton, or whoever it may be," Trump's campaign said in a statement.

Sanders hit back, saying: "Well, Mr Trump, what are you afraid of?"