Hundreds of demonstrators have blocked traffic outside a venue in California where Republican presidential hopeful Donald Trump was holding a rally.
A police car had its windows smashed as Mr Trump spoke inside a hall in the Orange County Fairgrounds in Costa Mesa. Some 20 arrests were made.
Mr Trump has vowed to deport millions of illegal immigrants if he is elected US president in November.
He faces strong opposition in parts of California, particularly among Latinos.
California, the biggest prize for Republican candidates in the nomination race, holds its primaries on 7 June.
On Tuesday, Mr Trump called himself the Republican "presumptive nominee" after five new primary wins in the states of Connecticut, Delaware, Rhode Island, Maryland and Pennsylvania.