Scott Walker's rivals see him as an up-and-comer in the Republican race for president, so they are focusing on the Wisconsin governor's changing positions on a number of issues.
The still-unofficial campaigns of several Republicans have assembled internal memos, research papers and detailed spreadsheets that highlight and track Walker's shifts on positions from immigration to ethanol to abortion. They say Walker has a broad pattern of flip-flopping that will be his greatest vulnerability.
The rush of what's known in political campaigns as "opposition research" comes as Walker is in the midst of a swing through two early voting states. He travels next week to South Carolina after spending this weekend in New Hampshire.
Steve Duprey, a Republican national committeeman from New Hampshire who is not aligned with any candidate, said Walker is relatively unknown among voters in his state - meaning the governor is subject to definition by his opponents.
"You have to be an authentic candidate," Duprey said. "If people think you're flipping left and right, that sticks with you."
Walker has leapt into the top-tier of the possible 2016 Republican presidential class after earning strong reviews for early performances in Iowa and at several forums. That's made him a target among his GOP competitors.
In the past week, aides working for other Republicans expected to run in 2016 have circulated materials that highlight Walker's change in position on ethanol mandates, among others. As a candidate for governor in 2006, Walker was critical of the requirement that gasoline contain a certain amount of corn-based ethanol. "Mandates hurt Wisconsin's working families," he said at the time. "And whether they are from Washington or Madison, we as fiscal conservatives should oppose them."
Speaking at an agriculture summit in Iowa last week, Walker said the fuel standard that requires the use of ethanol is "something he's willing to move forward on." His team says he still supports the gradual phase-out of the ethanol policy.
A former Republican National Committee chairman, Michael Steele, said he has heard from other Republicans about Walker's shifts on policy positions. Steele said it is a matter that will play in the presidential primaries.
"If you've taken positions and done things, you've got to stay true to that. You cannot reframe it for a presidential race," Steele said. "Everyone's trying to find a way to carve these men and women up before they even get out of the gate."
The AP contributed to this report.