If Trump does put an end to riots in Portland, and if he does so despite attempts by Wheeler (mayor and police commish at the same time as per longstanding Portland civic law) and Schmitt (county DA) to keep the nightly fun going, then one would like to believe Democrats themselves would credit him for upholding law and order over his own political gain.
Because make no mistake: the murders, beatings, arsons, and occasional forays into suburban Portland to harrass residents are helping Trump enormously.
A ticket organized around being a law and order prez certainly worked for Nixon in 1968, when Chicago burned during the Democrat convention there - not unlike the Pacific NW, Minneapolis, Chicago, NYC, and StL are all burning today.
Definitely a precedent in US history exists for overwhelming, silent electoral support for a GOP candidate of questionable character, under enormous fire otherwise, to win on a law and order ticket. See election of 1972 also.