Wisconsin Gov. Scott Walker (R) has recently surged to become one of the leading likely Republican contenders in the 2016 presidential race.

And his newfound status seems to have come with a series of pronounced changes to his past positions.

In Iowa last weekend, Walker announced a new stance on ethanol subsidies when he told voters in the corn-rich state he supports a federal mandate requiring that the corn-based biofuel be added to gasoline.

The pro-ethanol stance was a crowd pleaser for Walker when he addressed the Iowa Agriculture Summit on March 7, but his support for the Renewable Fuel Standard program is an apparent turn from his previous view that mandates are harmful to the economy.

It appears to be the latest in a series of policy shifts for the GOP rising star.

As he tightens his policy platform in the lead up to a possible 2016 presidential campaign, his past statements on several issues have also been called into question.

Here are three areas where Walker's positions have seemingly evolved:

Renewable Fuels Standard

In 2006, during his first, short-lived, unsuccessful campaign for Governor of Wisconsin, Walker said he would not support an ethanol mandate.

"It is clear to me that a big government mandate is not the way to support the farmers of this state," Walker said in a campaign radio ad.

"The free enterprise system must drive innovation to relieve our dependence on foreign oil, not mandates from the state or federal government."

On March 7 at the Iowa Agriculture Summit, hosted by agribusiness mogul Bruce Rastetter, Walker sang a different tune when he was asked about his views on ethanol.

"It's an access issue, and so it's something I'm willing to go forward on continuing the Renewable Fuel Standard and pressing the EPA to make sure there's certainty in terms of the blend levels set," Walker said, adding, "Now, long term — we've talked about this before as well — my goal would be to get to a point where we directly address those market access issues and I think that's a part of the challenge. So that eventually you didn't need to have a standard."

Update (6:05 p.m.): A spokeswoman for Walker's PAC, Our American Revival, disputed the notion that Walker changed his view on the Renewable Fuel Standard:

"Governor Walker opposed the establishment of a state mandate, but hadn't weighed in on the RFS. Speaking directly to the RFS as a potential candidate he has not and does not support the passage of new laws that require a specific percentage of ethanol use. He believes consumer choice should drive ethanol use, but first the EPA has to uphold the law on the books and set the level. Then, given the opportunity, he would work to address the root problem of market access and phase out the ethanol mandate. Additionally, he wouldn't get rid of it on day one because there’s a level of certainty that farmers and producers depend on and we have to factor that in when phasing it out."

Immigration

In 2013, Walker told the Wausau Daily Herald "it makes sense" to provide a pathway for illegal immigrants to be granted citizenship, hinting his support for amnesty.

However, on March 1, Walker acknowledged to Fox News that he has switched sides on the issue.

"My view has changed," Walker said.

Walker attributed his shift on amnesty to an increased awareness of the immigration system.

"I look at the problems we've experienced for the last few years. I've talked to governors on the border and others out there. I've talked to people all across America," Walker explained. "And the concerns I have is that we need to secure the border. We ultimately need to put in place a system that works. A legal immigration system that works. And part of doing this is put the onus on employers, getting them E-Verify and tools to do that. But I don't think you do it through amnesty."

Update: Walker's PAC spokeswoman clarified his views on immigration:

"He doesn't support amnesty and he's said he's learned more about this issue since Obama's unconstitutional executive action and he's seen how his fellow governors have had to deal with the collateral damage. He believes border security must be the top priority before we can have a conversation about anything else."

Right-to-work

In April 2012, Walker told Wisconsin Public Radio, "I have no interest in a right-to-work law in this state."

"We're not going to pursue that in the remainder of our term, and we're not going to pursue it in the future. The reason is private-sector unions are my partner in economic development," Walker said.

In spite of this pledge, on Monday, the Wisconsin Republican signed a right-to-work law that bans mandatory union dues at private sector businesses. Wisconsin is the 25th state in the U.S. with such a ban.

"We now have given one more big thing on that checklist to say that Wisconsin is open for business," Walker said this week, touting the new measure.

Update: Walker's PAC spokeswoman said he had long supported Right to Work legislation:

"He co-sponsored Right to Work legislation as a state legislator, said it wasn’t his first priority if he was to be reelected but when the state supported it through their representatives in the Assembly and Senate, he said he would sign it if it came to his desk which he did."