Police have radically stepped up security at Donald Trump's next campaign rally venue after yesterday's trouble in New Mexico.
Hundreds of people tried to storm the convention centre in Albuquerque where Mr Trump was speaking on Tuesday (US time) and clashed with riot police.
The presumed Republican presidential nominee is due to speak at a 7500-seater stadium at Anaheim in California later this morning, and CNN's Paul Buchanan reports police are out in force.
"What they have warned everybody today is if there is any violence, blocking of traffic, destruction of property, there will be arrests."
Many of the protesters in Albuquerque were flying Mexican flags. Police said they made arrests both outside and inside the rally, where protesters continually interrupted the billionaire New York developer's speech.
The police department's Twitter feed said officers were treated for injuries caused by thrown rocks.
"We respect the rights of everyone to protest and get their word out," Anaheim Police Sergeant Daron Wyatt said, adding they must do so "peacefully and within the confines of the law".
Meanwhile an investigation by US authorities has found his presumed Democratic rival Hillary Clinton failed to comply with State Department policies in her use of private email while Secretary of State.
It has criticised her for using private email for government business and for failing to turn over her records.
The findings aren't a legal complication for Ms Clinton, but could impact on her campaign to become President as it raises questions about transparency.