A ballot initiative to legalize marijuana in California could help propel endangered incumbent Sen. Barbara Boxer (D-CA) to re-election in November, according to a respected polling expert.

The presence of the pot legalization measure, Proposition 19, on the ballot is likely to entice many young Californians to vote in November when they otherwise would not have, declared Nate Silver of the New York Times on Wednesday evening. And young voters strongly lean Democratic, making them likely to pull the lever for Boxer.

Boxer, a three-term senator, is locked in a tight battle against former Hewlett Packard CEO Carly Fiorina, the Republican nominee. While the race has been virtually tied for weeks, Boxer has lately ticked up in the polls.

Silver explained the logic in his Times blog FiveThirtyEight (emphasis ours):

In California, there have been four polls released since last week’s forecast, all of which show material gains by the Democratic incumbent, Barbara Boxer. Ms. Boxer is now a 78 percent favorite to prevail in California, up from 58 percent last week. Although some of the California polls, like the one from Public Policy Polling, shows a voter sample that seems quite favorable to Democrats, younger voters may be more inspired to vote in California than elsewhere in the country because of the presence of a ballot initiative, Proposition 19, which would legalize possession of marijuana for personal use. The ballot initiative is favored to pass by most polls.

A survey by Public Policy Polling, a Democratic Party-affiliated firm, found Wednesday that 47 percent of Californians support the measure; 38 percent oppose it.

The same polling outfit revealed that Boxer has this week opened up a 50 to 42 point lead over Fiorina among likely California voters. It has a 3.9 percent margin of error.

Most lawmakers of both parties remain hesitant to endorse marijuana legalization -- including, ironically, Boxer herself, who told Talking Points Memo in April that it "could lead to an increase in crime, vehicle accidents and higher costs for local law enforcement agencies."

Progressive activists, however, have mobilized in favor of Prop 19, arguing that it could contain drug violence and generate tax revenues. Leading the charge in favor of the proposition is the "Just Say Now" campaign, a project of the liberal Web site Firedoglake.