Trip Gabriel for the NYT:

The divisive nominating contests have produced countercurrents of deep resentment in both parties. And next month, that bitterness could spill into the streets in large protests just when Republicans and Democrats — and the host cities — are trying to present images of unity to the country.

Mass demonstrations have occurred at nearly every modern political convention, perhaps none more disastrously than at the 1968 Democratic convention in Chicago, where street riots contributed to Hubert H. Humphrey’s loss that November.

There is no chance of that level of violence, officials in both cities insist, because modern policing has evolved to be less confrontational. Philadelphia is considering issuing $100 summonses to marchers blocking highways or failing to disperse, rather than arresting them.

But protest organizers in Cleveland say that by imposing strict rules to contain demonstrators, the city is only increasing the likelihood that unsanctioned protests will erupt, leading to violent clashes with the police or between Trump supporters and opponents.