Democrats tend to favor legalization the most. Many of them define it as an issue of racial injustice, citing statistics that show minorities are arrested at greater rates than whites for marijuana-related offenses.
It's also an issue that’s popular with two large voting groups in their party – minorities and youth – and one that Democratic candidates have touted on the campaign trail this cycle.
But there are Republicans who support legalization. They, however, tend to talk about the financial aspect, noting how the product that can boost their state’s coffers.
Republican Rep. Tom Garrett of Virginia, who introduced legislation last year that would take marijuana off the federal controlled substances list, said he changed his mind after meeting people who were helped by medical marijuana and, therefore, thought his agricultural-heavy state should benefit from it.
“Why, why, why are we importing nearly a billion dollars’ worth a year of industrial hemp from Canada when we can grow it better and create economic opportunities right here in Virginia? There's no good answer,” he said on a tele-town hall in February, according to a local news report.
An October Gallup poll found 64% of Americans supported legalization. Breaking that down, 72% of Democrats supported it while 51% of Republicans did.
Jon Gettman, an associate professor at Shenandoah University in Virginia who studies marijuana policy, said the lawmakers’ moves aren’t surprising.
“You have not only pronounced public support in terms of legalization,” he told ABC News, “you have demonstrated support with the initiatives passed and the emergence of state law.”
And marijuana has become legal in large states that are represented by powerful members of Congress such as California, Colorado, and Florida.
“We’re getting some significant stakeholders in the United States Congress now,” Gettman said.
And they're likely hearing from the voters back home.
“They’re probably getting a lot more contact from constituents asking why they aren’t protecting their states’ programs,” said Morgan Fox, the communications director for Marijuana Policy Project, a pro-legalization group.
“The time has come to decriminalize marijuana,” Schumer said in a statement. “My thinking – as well as the general population’s views – on the issue has evolved, and so I believe there’s no better time than the present to get this done.”
McConnell’s bill, known as the Hemp Farming Act of 2018, would remove hemp from the federal list of controlled substances and allow it to be sold as an agricultural commodity.
"By legalizing hemp and empowering states to conduct their own oversight plans, we can give the hemp industry the tools necessary to create jobs and new opportunities for farmers and manufacturers around the county," McConnell said in a statement last week.
The benefits of both sides’ argument – increased voter turnout and more revenue – can be seen in Colorado, the first state to legalize marijuana.
It saw a dramatic change in voting patterns between 2008 and 2012, the year the legalization initiative was on the ballot, according to a study from the Brookings Institute.
In 2008, 17% of self-described liberals voted. That number rose to 28% in 2012. More young people came out too for the initiative: in 2008, 14% of those aged 18 to 29 voted while it was 20% in 2012.
The state saw a boost in revenue too. The cannabis retail market generated $1.51 billion in sales last year and sales have totaled $4.5 billion since it was legalized in 2014, according to the Colorado Department of Revenue.
The drumbeat on full legalization has been heard across the country, ranging from the small states like Hawaii all the way to New York.
And several Democrats running for office this year have made the issue part of their platform.
At the National Cannabis Summit, Ben Jealous, the former president and CEO of the NAACP and a candidate for Maryland governor, noted legalization was a major part of his criminal justice strategy.
New York gubernatorial candidate Cynthia Nixon has called for its legalization, which she called a matter of “racial justice” when she spoke to a conference of progressives in Washington D.C. last week.
“We have to stop putting people of color in jail for something white people do with impunity,” she said.
Marijuana use is roughly equal among Blacks and whites, yet Blacks are 3.73 times as likely to be arrested for marijuana possession, the ACLU reported in a 2013 study.
Even in states like Florida, where medical use is legal, Democratic gubernatorial candidate Tallahassee Mayor Andrew Gillum pressed for its recreational use, citing the civil rights argument.
In a recent gubernatorial debate, he argued marijuana uses involves “over-criminalization of young people of communities of color.”
In Illinois’ gubernatorial race, Democratic candidate J.B. Pritzker said he would sign legislation to legalize marijuana if he wins.
And Texas Senate candidate Beto O’Rourke, a longtime supporter of the issue, tweeted about it on 420 day.
We must end the federal prohibition on marijuana in this country. — Beto O'Rourke (@BetoORourke) April 20, 2018
Republicans have been joining the conversation.
Some state GOP lawmakers in Michigan, which allows medical usage, are considering allowing personal possession through legislative action instead of a statewide initiative.
The reasoning, reports the Detroit News, are fears the measure would boost Democratic turnout in November.
And former Republican Speaker of the House John Boehner surprised political observers last week when he joined the advisory board of Acreage Holdings, one of the nation's largest cannabis corporations, saying "my thinking on cannabis has evolved" and that he now supports changing federal marijuana policy.
There are those who oppose legalization.
Kevin Sabet, the president of Smart Approaches to Marijuana, an anti-legalization group said science should guide policy.
“We need to slow this train down, we need to people before profit,” he said a press conference at the National Press Club on Friday. “And we need to get the science out about the truth about marijuana which every day is hurting more people as this country slides deeper into the legalization, really the commercialization of marijuana.”
“We don’t want to lock people up for using marijuana,” he added. “But to against criminalization isn’t to be for legalization.”
The administration will have ultimate authority on the federal legalization of marijuana as President Donald Trump would have to sign any congressional bill into law or set a federal policy initiative.
Some pro-legalization groups saw hope last month with Sen. Cory Gardner, R-Colo., announced he’d spoken to Trump, who agreed to support states’ rights on the issue.
“Since the campaign, President Trump has consistently supported states’ rights to decide for themselves how best to approach marijuana,” Gardner said in a statement. “Furthermore, President Trump has assured me that he will support a federalism-based legislative solution to fix this states’ rights issue once and for all.
These same groups were worried when, in January, Attorney General Jeff Sessions rescinded a trio of memos from the Obama administration that had a policy of non-interference with states when it came to marijuana use.
Republican Rep. Dana Rohrabacher of California, who is the lead sponsor of the Respect State Marijuana Laws Act, criticized Sessions when the decision was originally made. Rohrabacher has touted his support of marijuana in his competitive re-election campaign in a district that includes a lot of the state’s coastline.
“The attorney general of the United States has just delivered an extravagant holiday gift to the drug cartels,” he said in a statement. “By attacking the will of the American people, who overwhelmingly favor marijuana legalization, Jeff Sessions has shown a preference for allowing all commerce in marijuana to take place in the black market, which will inevitably bring the spike in violence he mistakenly attributes to marijuana itself.”
ABC News’ Cheyenne Haslett contributed to this story.