Sen. Marco Rubio (R-FL) is the third GOP presidential candidate of note to launch a campaign — and though he's spent just over four years in the Senate so far, he brings a very distinct set of policy proposals to the field.

Rubio's ideas are certainly closer to the GOP establishment's overall than Ted Cruz's or Rand Paul's. On foreign affairs and social issues, he's pretty near the Republican consensus. But he's pushed several innovative ideas, particularly on economic issues like taxes and student loan repayment. And he was a member of the "Gang of Eight" that wrote the Senate's immigration reform bill in 2013 — though since then, he's changed his tune on the issue.

Pair conservative tax cuts with a new tax credit for parents

Rubio already has a tax reform plan that exemplifies his approach to domestic and economic policy — he wants to pair existing GOP orthodoxy on tax cuts with proposals that would do more for ordinary people, rather than just the wealthy. The plan, co-authored with Sen. Mike Lee (R-UT), would dramatically flatten and simplify the tax code — removing all deductions except those for mortgage interest and charitable giving, and creating only two income tax brackets. It would also eliminate taxes on capital gains and dividends — long a popular proposal on the right.

His plan's main innovation, though, is a new $2,500-per-child tax credit for parents. This is, in part a political strategy to craft a Republican economic policy that does more for the working class and middle class (though the credit wouldn't apply to families with very low incomes). The addition of a new, expensive tax cut also means Rubio's plan would hugely increase the deficit. Learn more about it from Dylan Matthews here.

Once an immigration reformer, Rubio now argues that border security should come first

In 2013, Marco Rubio was perhaps the most important Republican member of the bipartisan Gang of Eight senators crafting an immigration reform bill. The group's proposal would create a path to citizenship for most unauthorized immigrants, provided they met certain requirements, as well as increasing spending on border security and toughening requirements on employers to verify that their workers have legal status.

But though the bill passed the Senate, its lack of conservative support doomed it in the GOP-dominated House. Rubio himself became convinced, he now says, that it's impossible to "have a conversation" about legalizing the status of unauthorized immigrants until Americans are convinced the border is secure. If you read between the lines of his recent remarks, he hasn't quite backed off from his reform policies — but he mainly says the time isn't right now. So don't expect him to make immigration reform a focus of his campaign.

A foreign policy hawk

The Republican Party is debating the future of its foreign policy, but Rubio has long made his views clear: he's a hawk. He's consistently criticized Obama's foreign policies for being too weak, called for more defense spending, and argued for more US intervention abroad rather than less. Indeed, Reason's Matt Welch called Rubio "the anti-Rand Paul on foreign policy."

Rubio pushed for military action against Libya in 2011 before the Obama administration did. He's said that the tumult in Syria is "a vital national concern," and pressed for arming anti-Assad Syrian rebels. However, when Obama sought congressional authorization to strike Assad over his use of chemical weapons in late 2013, Rubio voted against it in committee, saying, "I remain unconvinced that the use of force proposed here will work."

When ISIS gained strength in 2014, Rubio pressed for military action against the group. And when Obama's airstrikes against ISIS seemed ineffective, Rubio pushed for more, saying, "You cannot defeat an army on the ground simply from the air."

On Iran, Rubio's said the only deal he'd support is one in which the country wouldn't be allowed to enrich any uranium — a position many foreign policy experts believe would make a deal impossible. He's criticized Obama for being insufficiently supportive of Israel. And he's blasted Obama's proposal to end the embargo against Cuba, saying that it would strengthen an oppressive regime.

Base student loan repayment on the borrower's income

Rubio's supported a bill that would, in Libby Nelson's words, "end the complicated current system of student loan repayment in favor of basing loan payments on borrowers' income." It would also have payments be collected automatically by the federal government, rather than student loan servicing companies. Read more from Nelson here.

Doesn't believe humans are causing climate change

Rubio doesn't believe the scientific consensus that human activity is the main cause of dangerous global warming — and he doesn't support action to curb emissions. "I do not believe that human activity is causing these dramatic changes to our climate the way these scientists are portraying it," Rubio said in 2014. "And I do not believe that the laws that they propose we pass will do anything about it, except it will destroy our economy." In other interviews, Rubio has said that his own views on climate science don't matter because he's "not a scientist."

Pro-life

Rubio is pro-life and has supported a bill to ban abortions after 20 weeks of pregnancy. "The science is settled, it’s not even a consensus, it is a unanimity, that human life begins at conception," he's said. He's also argued that "the issue of life" is "a basic core issue that every society needs to answer," and "a fundamental one that trumps virtually any other right that I can imagine."

Against same-sex marriage, but thinks states should get to decide

In a 2014 speech, Rubio called himself "not anti-gay but pro-traditional marriage." He's also said that "thousands of years of human history have shown that the ideal setting for children to grow up is with a mother and father." He continued: "I believe the union of one man and one woman is a special relationship that has proved to be of great benefit to our society, our nation, and our people, and therefore deserves to be elevated in our laws." He's said that if people want to push same-sex marriage, the way to do it is "go through the legislature" or "go on the ballot" — not through the courts.

Big changes for Medicare and Social Security

Rubio has called for spending-reducing reforms for Medicare and Social Security, saying that without major changes, those "programs will cease to exist certainly as we know them." He’s backed Paul Ryan’s plan to move Medicare to a "premium support" system, where seniors are given a fixed amount of money that they can use "to purchase health insurance from either Medicare or a private provider." And he’s called for gradually increasing the Social Security retirement age to bring it more in line with modern life expectancies, and for means-testing Social Security benefits so richer retirees get less. These reforms would apply to future, not current, retirees.

Don't loosen drug laws

While other GOP contenders have called for loosening penalties for nonviolent drug offenders, Rubio has not. "Reform should not begin with careless weakening of drug laws that have done so much to help end the violence and mayhem that plagued American cities in prior decades," he wrote in an October 2014 op-ed. He has also said that marijuana "is not good for the country," and that he thinks there's "no responsible way to recreationally use" it.