After months of social-justice activism that made Portland a vivid, sometimes violent focal point for a nation debating the same issues around police accountability and reform, the movement here has splintered into bickering groups, at odds over tactics, goals and an overall direction for how to make the city safer, with the police force still at the debate’s bitter center. The sharpening conflict between rising violent crime and efforts to reduce the size of police departments has played out across the American West throughout this pandemic year. Now cities such as Portland, considered among the most ambitious in moving to reshape its police force, have retrenched. So have Oakland, Calif.; Berkeley, Calif.; Los Angeles and several other influential cities on the issue. The nightly confrontations with police and federal agents deployed here by President Donald Trump have been replaced by a kind of generational hopelessness, a tenuous sense of security across an under-policed city and a return to an old-school style of gun violence reminiscent of a tit-for-tat cycle of deadly reprisals, almost always among young men of color. Through April, the police reported 348 shootings, more than double those recorded over the first four months of last year.