There have been a number of hot-button issues that have dominated the early Republican debates, and even the Democratic Party's lone debate, but none have arguably garnered more attention than marijuana.

There may be far bigger issues at hand than marijuana, such as the U.S. economy, foreign relations, immigration, and Social Security, but the public has made it very clear that it expects the next president and Congress to lay out a path toward an eventual legalization of marijuana. The last three national polls -- Gallup, Pew Research, and General Social Survey -- have all shown that a slim majority of Americans share a favorable view of marijuana, and smaller, independent polls have suggested there is very strong support for the legalization of marijuana for medicinal purposes.

All told, given the above, we shouldn't be too surprised that nearly two-dozen states have legalized marijuana for medical use and another four states allow the currently illicit drug to be sold for recreational purposes. As President Obama has previously suggested, having residents of additional states approve the legalization of recreational marijuana could go a long way to pushing Congress's hand toward reforming federal marijuana laws.

Three states that could legalize recreational marijuana in 2016

Although it's still completely up to debate, dependent on the number of signatures collected, and will generally vary state-by-state depending on the percentage of "Yes" votes required, here are three states that I believe are primed to legalize recreational marijuana in 2016. Please note that just because I believe these states are primed to legalize recreational marijuana, it doesn't mean it will necessarily be legalized. I'm merely pointing to possible points of expansion for the marijuana industry in 2016.

1. California

California seems like a logical choice considering that the passage of the Compassionate Use Act of 1996 (known as Proposition 215) allowed medical marijuana to be prescribed by physicians for the first time ever. As a marijuana revolutionary, and a noted progressive state, residents appear to be well in support of legalizing the drug across the board. According to CheatSheet.com via a Tulchin Research poll, almost two-thirds (65%) of respondents are in favor of its legalization.

In 2014, the Marijuana Policy Project of California filed the appropriate paperwork needed to form a campaign committee and will work toward formally putting marijuana on the 2016 ballot. A "Yes" vote in California, which would be the world's eighth-largest economy if it were its own nation, could mean big money rolling into the marijuana industry and could set a precedent for other states to follow. Congress's ability to track the success of California in regulating its marijuana industry (if recreational legalization is passed) could serve to remove one of the many hurdles currently holding lawmakers back on Capitol Hill from changing their stance.

2. Nevada

Already one of the 23 states to have legalized medical marijuana, the U.S. casino mecca could very well become a recreational-legal state following next year's elections.

Led by the Coalition to Regulate Marijuana Like Alcohol in Nevada, the 2016 recreational marijuana initiative is already on the ballot. At the moment Nevada is the only state to hold that distinction for 2016. The Coalition was tasked with collecting the required 101,667 signatures by Nov. 11, 2014 in order to get the initiative on the ballot by 2016. The group eventually turned in around 200,000 signatures, handily passing the total needed to put the measure in front of state legislators. With no action being taken by the Nevada legislature in 2015, the measure has been locked onto the ballot for Nevada residents to vote upon in 2016.

As with most other states, Nevada's legalization will allow up to one ounce to be sold to adults ages 21 and up, and the tax revenue generated would be used to fund education within the state.

3. New York

Like California, New York is another large and progressive state that would serve as the perfect testing point for state-level industry regulation. New York already has an established medical marijuana industry, albeit it's the state that most recently legalized medical marijuana, which it did in the summer of 2014.

What makes New York the perfect point of entry for the recreational marijuana industry is that it isn't a referendum state. In layman's terms this means legislators don't have to put a marijuana initiative in front of New York residents in order to pass it. If a bill gets through the legislature and is signed into law, it goes into effect immediately.

The Marijuana Regulation and Taxation Act has already been introduced in the New York state legislature, but it's yet to gain the necessary traction to be turned into law. As Rolling Stone noted in June, current governor Andrew Cuomo has been the primary obstacle due to his general silence on the issue and varying stance on the drug over the years. However, with medical marijuana now signed into law, and Cuomo wanting to keep his constituents happy, a bill legalizing recreational marijuana is certainly on the table at this point.

In addition to the aforementioned three states, the following states also have active coalitions looking to raise capital and obtain signatures to get recreational marijuana initiatives in front of voters or in front of state lawmakers by 2016: Maine, Massachusetts, Arkansas, Arizona, Vermont, Missouri, Wyoming, Montana, Michigan, Connecticut, Maryland, Minnesota, Rhode Island, and Delaware. It's a pretty long list.

Keep this in mind

The marijuana industry has an abundance of expansion opportunities in 2016 and beyond, but it's important to keep in mind that even if recreational marijuana expands to a bunch of new states in 2016, marijuana business may still struggle to survive over the long run.

The marijuana industry has an exceptional number of challenges that it's yet to overcome, and the only true recipe is for change at the federal level. Truth be told, no one is exactly sure when, or if, that'll ever happen.

For instance, marijuana industries currently have minimal access to basic financial services. Checking accounts and lines of credit are extremely difficult to come by for marijuana businesses since the loopholes required for banks to service the marijuana industry are extensive. Banks would rather not risk the potential of getting caught on the wrong side of federal law, and therefore they have, for the most part, stuck to the sidelines.

Marijuana businesses are also facing a very unfavorable tax situation. A provision within the U.S. tax code disallows marijuana businesses from taking deductions on expenses that normal businesses would be able to deduct. This means marijuana businesses are giving a lot of their profits back to the federal government in taxes, which makes expanding a difficult proposition.

While I fully expect marijuana to remain a hot-button issue in the years ahead, it doesn't mean that marijuana will make for a viable long-term investment opportunity anytime soon. There still appear to be far too many federal obstacles in place, making marijuana among the riskiest investments imaginable.