The unlikely pitch from medical marijuana legalization advocates to conservatives who control the Florida Legislature goes like this: Pass a law now — or risk hurting the GOP presidential candidate by having a referendum on the 2016 ballot.

A constitutional amendment would draw to the polls the younger, more liberal voters more likely to support medical pot, proponents say, helping the eventual Democratic nominee in the nation's largest swing state — possibly over Jeb Bush or Marco Rubio, both homegrown Republicans.

"Most people understand that, in a presidential year, medical marijuana will pass," said Jeff Kottkamp, the Republican former lieutenant governor who backs legalization. "They also know on the national level a Republican can't win without Florida."

But GOP leaders in Tallahassee aren't buying it. Medical marijuana supporters made a similar contention when the issue was on the ballot last year — both Rubio and Bush opposed it — yet Republican Gov. Rick Scott defeated Democrat Charlie Crist anyway. Many Crist voters didn't vote for the marijuana amendment, a post-election analysis showed. In fact, statewide ballot measures have failed to sway presidential elections in Florida time and time again.

The broad use of marijuana for medicinal purposes remains illegal — despite receiving support from nearly 58 percent of voters in November — because the state has a 60 percent threshold to adopt constitutional amendments.

"I really don't think that it would ultimately impact the presidential campaign," said state Sen. Jeff Brandes, the St. Petersburg Republican who proposed this year's medical cannabis legislation in the Senate, SB 528. "I just think it's the right policy."

If no law is passed, legislators could again take it up in early 2016, well before the November 2016 election. But by then, the campaign for a constitutional amendment would already be under way, organizers say. They plan to tweak its wording and ramp up petition signature-gathering after this year's session, which is scheduled to end May 1.

Last year, lawmakers authorized one marijuana strain, known as Charlotte's Web, which is low in THC — the high-inducing chemical — yet still beneficial for patients with cancer or severe epilepsy. Between lengthy rule writing for growing and distributing pot, and the legal challenges that have come with it, Charlotte's Web probably won't be available in Florida before next year.

Key Republicans who signed off on the strain want the state to implement the law and see how it goes before agreeing to any expansion, which they consider politically motivated to help Democrats.

But the existing law is so restrictive that Florida doesn't figure among the 23 states that have allowed medical marijuana, so the United for Care group that campaigned for last year's ballot amendment intends to bring one to voters again in 2016 — unless legislators act first.

Four days before the annual lawmaking session began March 3, Florida for Care gathered about 25 supporters at the Westin Colonnade Hotel in Coral Gables for a policy conference that included an update on the legislation's odds in Tallahassee. Ben Pollara, Florida for Care's executive director, said passing a bill would be difficult and urged attendees to trek to the state Capitol to make their case.

"It's a long 60 days, and a lot can change," Pollara said of the session.

Now into the session's third week, the proposal has yet to get on any committee agendas in the Senate or the more conservative House of Representatives.

"Politically, it's a tough issue in the House," said Rep. Greg Steube, a Sarasota Republican and sponsor of the House bill, HB 683. "I'm hoping that Sen. Brandes can get it up and get it moving in the Senate."

Brandes said, "The window of opportunity for the Legislature to act is closing."

Even some Democrats who endorse the law see a rocky path ahead.

"The Legislature should act, but it doesn't feel like there's a lot of momentum to pass," political consultant Steve Schale said.

Like the Republican legislators, he disputed the notion that trying to draw a line between a medical marijuana ballot initiative and the presidential race would be persuasive.

"There's just no evidence in the history of Florida of there having been an up-ballot impact" from a constitutional amendment, he said.

Schale noted that Republican George W. Bush won Florida in 2004 — the same year a ballot amendment raising the minimum wage was thought to attract liberal voters (the initiative passed). Likewise, Democrat Barack Obama won four years later when a ballot amendment banning same-sex marriage was supposed to draw conservative voters (that proposal also passed, though the law amendment has been ruled unconstitutional).

Without a clear link between a voter's presidential and constitutional amendment picks, the stronger case for legislative action on medical pot this year is the one being made by the bill's Republican sponsors: that the only way for the state to be in control is by writing the law themselves.

"It would be smart for the Legislature to expand on Charlotte's Web and allow a tightly controlled expansion of medical marijuana that would help those patients that really need it," said Javier Correoso, a Republican who helped run the campaign against last year's ballot initiative for Drug Free Florida.

"Timing is of the essence. The Legislature has to do something to protect our community because if it passes in 2016, it's going to be impossible to regulate it."

Contact Patricia Mazzei at pmazzei@MiamiHerald.com.