Medical marijuana is not only doing well in public opinion surveys, but it could get an unexpected and unintended boost from its most high-profile opponent: Gov. Rick Scott.

In an ironic twist, Scott's re-election campaign is set to spark such a mammoth TV ad war that it threatens to reduce the supply of available commercial advertising time, drive up the price of commercials and, therefore, make it tougher for outgunned antidrug crusaders to get out their message.

"In an environment such as that, message-penetration can be challenging for anyone who doesn't have a lot of money," said Kyle Roberts, president of Virginia-based Smart Media Group, one of the nation's premier political ad-buying firms.

The estimated $150 million that could be spent — $100 million from Scott and Republicans; $50 million from Democrat Charlie Crist — "can cause a lot of voter confusion when it comes to other issues on the ballot," Roberts said.

Medical marijuana is so popular in Florida that 78 percent of likely voters in Republican-controlled state Senate districts back the idea, according to a recent state GOP poll obtained by the Miami Herald.

The survey echoes two others last month that found support for medical marijuana ranging from 64 percent to 70 percent — results consistent with every major Florida public poll released in the past year.

Opponents of medical marijuana have one major advantage, however: It takes 60 percent voter approval — a high bar — to pass a constitutional amendment in Florida.

So far, 20 states and Washington, D.C., have decriminalized marijuana, most for medical reasons.

The Republican state Senate district poll, conducted last month by the Tarrance Group, found that 47 percent of likely voters favored outright legalization and 48 percent opposed legalization. And voters strongly backed lighter prison sentences for nonviolent drug offenders.

In a nod to the popularity of the issue — and his own struggles in public opinion surveys — Scott hasn't crusaded against the proposed amendment. He said he's opposed to the medical marijuana initiative because he's against illegal drugs. However, he hasn't explained why he would oppose legalized marijuana if it's shown to have real medical benefits.

Despite the trends in favor of marijuana decriminalization in one form or another, some surveys show, the argument that medical marijuana leads to complete legalization can be a potent tool to defeat the proposed amendment.

But to get their message out effectively, opponents need to advertise on TV in Florida due to the state's large size and diverse media markets. And ads are expensive.

It can cost a political candidate nearly $2 million a week to run enough statewide ads so that the average viewer sees them 10 times. For political committees, the cost of such a media buy can be about double what it costs candidates, who get the lowest-priced rates.

Also, due to the broad array of TV choices and channels, voters are tougher to reach and persuade nowadays, requiring ever-more sophisticated efforts to identify the right way and time to reach them.

Add it all together — the lack of ad time, the higher costs and the popular polling for medical-marijuana — and antidrug crusaders know they face a tough campaign.

But they're still going to try, according to Lana Beck, spokeswoman with St. Petersburg-based Drug Free America Foundation Inc. and Save Our Society From Drugs, the lead organizations opposed to the amendment along with law-enforcement agencies.

"We will be educating at the grass roots level," Beck said.

John Morgan hopes the opposition stays that way.

"If this is a word-of-mouth campaign, a grass roots effort, we win," said Morgan, an Orlando trial lawyer funding and leading the effort through his group People United for Medical Marijuana.

Morgan has a secret weapon: the $20 million in TV ad time he reserves annually for his Morgan & Morgan firm, which employs Crist. Morgan said he's prepared to swap out some of his firm's air time for ads for medical marijuana should he need to.

For years, the GOP-led Legislature has blocked and even refused to hear bills on the topic.

But this year, Republican lawmakers have backed a bipartisan bill that would legalize a strain of marijuana for people with severe epilepsy. But it doesn't address other so-called debilitating ailments — such as cancer, AIDS or glaucoma — targeted by the constitutional amendment.

The Senate poll indicated support for Charlotte's Web stood at 79 percent in favor, 18 percent opposed — mirroring support for the broader medical marijuana effort. Compared with a similar GOP Senate poll in April, support shifted a net 24 percentage points in favor of Charlotte's Web.

Voters by 65-28 percent favored reducing prison sentences for nonviolent drug offenders and, by 78-15 percent, they supported prison diversion programs for those convicted of nonviolent crimes.

Some Democrats, such as state Sen. Dwight Bullard of Miami, want to legalize marijuana outright, as Washington state and Colorado did.

That bill has a slim chance of passing in the Legislature. Even Morgan, a Democrat, opposes the Democratic legalization effort because, he said, it could be used as a political weapon by opponents who say the medical marijuana amendment is a Trojan horse for recreational pot use.