Trump's remarks Friday echo a promise that Gardner said he received privately from the president in April to support legislation protecting the marijuana industry in states that have legalized the drug.
"My legislation is in line with what President Trump said on the campaign and what he and I have discussed several times since he was elected," Gardner said in a statement Friday. He welcomed the president's "continued interest in an approach that respects the will of the voters in each state."
Another co-sponsor of the measure, Democratic U.S. Sen. Elizabeth Warren of Massachusetts, said in a statement that Washington "needs to get out of the business of outlawing marijuana."
California, home to one in eight Americans, launched the nation's largest legal marijuana marketplace on Jan. 1 but thousands of businesses that have been licensed are still facing the threat of federal prosecution.
A major problem stemming from the federal ban: Major banks have been reluctant to do business with marijuana companies, fearing it could lead to prosecution. In California, for example, paying taxes and other transactions are often done in cash, sometimes in vast amounts.
The bill includes language intended to address financial issues caused by the federal ban.