Washington (CNN) Scott Walker on Sunday took his third position within seven days on Donald Trump's proposal to end birthright citizenship, this time saying he opposes Trump and supports the policy.

The Wisconsin governor and Republican presidential candidate was asked on ABC's "This Week" whether he backs Trump's push to end the 14th Amendment's mandate that all children born in the United States are automatically granted citizenship.

"Well, I said the law is there. And we need to enforce the laws, including those that are in the Constitution," Walker said, adding that he favors addressing illegal immigration by improving border security and requiring businesses to use a system called E-Verify to check workers' legal status.

ABC's George Stephanopoulos pressed further, asking: "So you're not seeking to repeal or alter the 14th Amendment?"

"No," Walker said. "My point is, any discussion that goes beyond securing the border and enforcing the laws are things that should be a red flag to voters out there, who for years have heard lip service from politicians and are understandably angry because those politicians haven't been committed to following through on those promises."

It's a different answer than the one Walker gave Monday at the Iowa State Fair.

Asked by MSNBC's Kasie Hunt whether birthright citizenship should be ended, he said then: "Yeah, absolutely, going forward."

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Walker cited Nevada Democratic Sen. Harry Reid's support for ending the policy -- in the early 1990s introduced legislation that would have revoked the 14th Amendment's guarantee of citizenship for U.S.-born children. Reid has since reversed that position.

"Yeah," he said on Monday at the fair. "To me it's about enforcing the laws in this country. And I've been very clear, I think you enforce the laws, and I think it's important to send a message that we're going to enforce the laws, no matter how people come here we're going to enforce the laws in this country."

Then, on Friday, Walker offered another stance -- telling CNBC's John Harwood that he won't weigh in on birthright citizenship.

"I'm not taking a position on it one way or the other," he said in that interview.

The changing answers come as Walker's standing in polls -- particularly in Iowa, which his campaign regards as crucial to his chances of winning the GOP nomination -- has been hurt by the rise of Trump and other outsider candidates, like retired neurosurgeon Ben Carson and former Hewlett-Packard executive Carly Fiorina.

Walker has made an effort to play up his status as an outsider -- a politician who came up through Milwaukee and Wisconsin politics, with no ties to Washington.

He has attempted to avoid confronting Trump directly, saying his own immigration views are "similar" and launching new broadsides at the Republican-led Congress in recent days.

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Trump directly attacked Walker on Sunday during his own appearance on ABC's "This Week," citing Wisconsin's budget woes.

"I'm honored that he wants to copy me and he's a nice man. ... I gave him campaign contributions when he was running for governor. I like him very much," Trump said.

"But his state has not performed well," he said. "We need somebody that's going to make it perform well, this country perform well."

Given a chance to respond to Trump Sunday on "This Week," Walker accused the real estate mogul of making the same arguments Democrats in Wisconsin have in recent years.

"Those are the same talking points the Democrats used. They didn't work in the past. They're not going to work now," he said.

Then, Walker pivoted to a broader anger represented by Trump's ascent to the top of national GOP polls.

"But the one thing that I do want to clarify is I do think that there is some real frustration out there," Walker said. "It's way you not only see his numbers up, you see some of the other candidates who have not run for office before. They're angry at Washington. Heck, I'm angry at Washington. I'm angry at my own -- my own party leadership, who told us they were going to repeal Obamacare and we still don't see a bill on the desk of the President. I think that's where the real frustration is."