A vice president has to defer to the president's decisions on policy, but vice presidents can also help shape it. Dick Cheney pushed George W. Bush to invade Iraq, and Joe Biden gave Barack Obama a nudge to endorse same-sex marriage. Maybe Kamala Harris will convince Biden to push for legalizing marijuana.

There are reasons to think so. One was her laughing reply last year when an interviewer asked if she had ever smoked cannabis: "Half my family's from Jamaica. Are you kidding me?" Another is that as attorney general of California, she endorsed legalization of recreational weed, which the state's voters approved in 2016.

She is also the lead sponsor on legislation to lift the longstanding federal ban on cannabis. Her bill would remove marijuana from the Controlled Substances Act, leaving its status up to individual states, while authorizing expungement and sentencing review for those previously convicted of federal cannabis offenses. That Harris introduced this measure during the presidential campaign suggests she's genuinely committed to the change — and unafraid of the controversy.

Her bill targets an exasperating anomaly. States are fully entitled to outlaw and punish marijuana use, but they have only limited authority to allow it. That's because of the federal government's ban. It can go after cannabis consumers and suppliers even in states that have legalized pot.

That happens to be most of them. This year, Illinois became the 11th state (along with the District of Columbia) to allow recreational use by adults. Medical use is sanctioned in 33 states. Most Americans now live in states that provide legal access.

But we all live in a nation that doesn't. No matter what a state does, or tries to do, the federal government retains the ultimate power. And that fact hangs ominously over everything.

Under both George W. Bush and Barack Obama, the federal Drug Enforcement Administration raided state-approved medical marijuana shops and prosecuted their owners. Not until 2013, did Obama's Justice Department issue a memo telling federal prosecutors to back off.

As attorney general under Donald Trump, Jeff Sessions made a big deal of scrapping that policy. His successor also has the mindset of an undercover narc. In June, a Justice Department lawyer came forward to accuse William Barr of harassing legal cannabis companies with unjustified antitrust investigations because of his "personal dislike of the industry."

Removing the federal threat would make it much easier and safer for companies to operate in the legal pot sector, and for financial institutions to treat them like normal businesses. It would free every state to make its own choices without chronic fear of the federal hammer.

Democrats need no convincing. Almost every candidate in the presidential primaries came out in favor of legalizing pot at the federal level.

They have the public overwhelmingly on their side. A Gallup Poll last year found that 66 percent of Americans — and 51 percent of Republicans — think marijuana use should be legal, period. People of every age group agree, with the exception of those 65 and older, who were split 49 percent to 49 percent.

But one candidate has yet to be persuaded: Biden. He has moved in that direction, endorsing decriminalization of recreational use, legalization for medical use and expungement of convictions. He also supports classifying cannabis as a federal Schedule II drug, which is reserved for dangerous drugs that have medical value, instead of its current Schedule I.

That's the big difference between him and Harris, whose bill would "de-schedule" marijuana — removing it from the Controlled Substances Act and leaving the matter up to the states. Re-scheduling, by contrast, "means retaining criminal penalties for possession without a prescription," Justin Strekal, political director of the National Organization for the Reform of Marijuana Laws, told me.

Biden may not be willing to adopt a more liberal stance before November, if only because his lead in the polls gives him no reason to change. But though the onetime drug war supporter is not there yet, he has already gone all but the last mile. If he gets to the White House, he will have Harris to escort him the rest of the way.

She, after all, has gone so far as to say of cannabis, "I think it gives a lot of people joy, and we need more joy in the world." If she can persuade President Biden to follow her lead on marijuana, there will be plenty of joy to go around.

Steve Chapman blogs at http://www.chicagotribune.com/news/opinion/chapman. Follow him on Twitter @SteveChapman13 or at https://www.facebook.com/stevechapman13. To find out more about Steve Chapman and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.