The legalization of marijuana is a more mainstream issue now than it has ever been. That trend is both reflected and powered by the advocacy of people like Rick Steves, the mild-mannered travel writer and host of “Rick Steves’ Europe,” who campaigned for legalization in his home state of Washington in 2012 and now travels the country doing the same thing.

A 2017 Gallup poll found a majority of Americans — 64 percent — now support legalization of the drug in some form, including 51 percent of Republicans. While it remains illegal at the federal level, nine states plus the District of Columbia allow recreational use of the drug, and 30 states, D.C., Puerto Rico and Guam have comprehensive medical marijuana laws.

Medical marijuana is on the ballot in Missouri in November, and a political compromise reached earlier this month in deep-red Utah may pave the way for it there, too. Voters in North Dakota and Michigan will decide on recreational use of the drug.

Mr. Steves discussed his advocacy, his travels and the ballot initiatives. This interview has been condensed and edited for clarity.