Nearly two-in-three Americans now support the legalization of marijuana, a four percent jump in just one year and the largest support Gallup has found in almost a half-century of polling.

Marijuana is still illegal under federal law. But with more states approving legalization in each election season, about 20 percent of Americans now live where marijuana use is legal.

The newest poll, released this morning by Gallup, was conducted Oct. 5-11 involving 1,028 adult Americans. It found that 64 percent of them now support marijuana legalization. When Gallup first asked the question in 1969, only 12 percent did.

Support rose to 28 percent in 1978, then held generally steady in the mid-20-percent range through the 1980’s and 1990’s. In 2002, it jumped to 34 percent and with a couple of minor dips, has been generally rising ever since. It passed 50 percent in 2013 and 58 percent the next year.

Of course, a majority of Democrats has long supported legalization. You’d expect that. But this year for the first time a majority of Republicans joined in (51 percent), up nine percentage points in just the last year.

Gallup notes that the growth of support for marijuana legalization has generally followed growth of support for same-sex marriage:

On both issues, about a quarter supported legalization in the late 1990s, and today 64% favor each. Over the past several years, Gallup has found that Americans have become more liberal on a variety of social issues.

Perhaps inadvertently, the Gallup writer let slip where he stands on the issue of legal pot use: “More than one in five Americans live in a state where they can legally enjoy use of the drug.”