Des Moines, Iowa(CNN) Hillary Clinton's presidential campaign is challenging Bernie Sanders' consistency on a host of issues in the run up to the Iowa caucuses, hitting her Democratic rival in an area that many of his die-hard supporters feel differentiates the two candidates.
And so far, the effort is getting results.
Clinton's campaign, in the last week, has compelled Sanders to disavow a 2005 gun vote, break a pledge not to raise taxes on the middle class in his healthcare proposal and backtrack on his call for Iranian troops on the ground in Syria.
The latest skirmish in this effort -- the Clinton campaign's attempt to cast the Vermont senator as a foreign policy lightweight regarding Iran and Syria -- reached a pinnacle on Thursday when Sanders told The New York Times that he never called for Iranian troops on the ground in the war-torn country.
"No," Sanders said when asked whether he called for Iranian troops in Syria. "What I have said is that I would like to see -- and I understand, believe me, that Iran and Saudi Arabia hate each other -- but, to the degree that we can, create a process where Muslim countries can come together to fight ISIS."
But at November's Democratic debate, Sanders said that Muslim nations around Syria, namely "Saudi Arabia, Iran, Turkey, Jordan" had to step up and "get their hands dirty, their boots on the ground" in order to "take on ISIS."
On Friday, Sanders' spokesman Michael Briggs declined to engage on whether the senator ever called directly for troops on the ground in Syria but said his position on ISIS and Syria was that "Iran should be part of a coalition of Middle East nations."
It is questionable whether the Clinton campaign's strategy will work with voters, however. Many Sanders supporters already view him as someone who has been consistent for much of his 30-year career and believe it is Clinton -- a former first lady, senator and secretary of state who has admittedly "evolved" on certain issues -- who lacks consistency.
"There is a real double standard when it comes to me," Clinton said earlier this month about how she moved from opposing same-sex marriage to supporting it. "Everyone else can evolve."
Undecided voters and Sanders supporters have mixed feelings about the issue of consistency.
"He is just so passionate and I think the way he talks really just speaks to my age group," said Emily Arvola, an undecided senior at the University of Iowa who turned out for Clinton's concert with pop star Demi Lovato on Thursday. "He is new and exciting and you can tell how much he cares when he talks."
Others in the audience, including a handful of Sanders supporters, said young voters are looking for someone who doesn't waver, and they believe Sanders is that candidate.
"I am fairly decided," said Connor Johnson, 17, who will be eligible to caucus on February 1. "Bernie has been very consistent on his views for a long time and that means a lot to me."
Clinton, Johnson said, had not been as consistent in his mind and, at times, makes people feel like it is "her time" to be president.
Even so, Clinton's campaign is confident that there is enough time to change the way people in Iowa and New Hampshire view the senator -- reflected in the intensity with which its focusing on his record.
Earlier this month, Sanders backed away from a 2005 vote that gave gun manufacturers immunity from prosecution, announcing in a press release that he supports a proposed bill that would amend that vote. The position, which came after considerable pressure from Clinton and her aides, is a reversal from statements Sanders and his aides have made throughout the campaign.
And then, just a day later, Sanders released his Medicare-for-all healthcare plan, under pressure from Clinton and her aides to do so before voting starts on February 1.
The plan, despite Sanders' pledge to only raise middle class taxes to pay for paid family leave, would be financed by a 2.2% income tax on all Americans and a 6.2% levy on employers.
Sanders has argued that tax hikes are worth it to achieve universal coverage.
But Clinton's press secretary seized on Sanders' healthcare plan as chance to cast the senator as a flip flopper.
"Senator Sanders has been changing a lot of positions in the last 24 hours, because when his plans and record come under scrutiny, their very real flaws get exposed," Clinton spokesman Brian Fallon said in a statement. "When you're running for President and you're serious about getting results for the American people, details matter -- and Senator Sanders is making them up as he goes along."