Donald Trump's shake-up of his legal team this week suggested he is prepared to go to war with special counsel Robert Mueller. As observers of all stripes assess potential outcomes for the president, Republican voters are cheering Trump on, signaling that the longer the investigation continues, the more they see themselves as fellow soldiers in his battle with an overreaching prosecutor.

The Trump-Mueller clash is intensifying as primary voters head to the polls in key races that will ultimately shape the balance of power in Congress. Candidates seeking the Republican nomination next week for U.S. Senate seats in West Virginia and Indiana, for example, have been echoing Trump's "witch hunt" rhetoric. And party strategists say base voters could be motivated not just through the primary season but into the general election by the continued investigation, which they perceive to have ventured beyond its mandate -- and was possibly unwarranted in the first place.

"This is a battle between the forces of permanent Washington and the forces of voters outside of Washington," said Dallas Woodhouse, the executive director of the Republican Party of North Carolina. "Voters see themselves in this fight with the president. ... They do not like being told by the Democrats that they are gullible and stupid and manipulated by the Russians."

The Mueller probe has produced over a dozen indictments, including guilty pleas from Trump associates for lying to investigators, and the administration has approved new sanctions against Russia amid evidence of election meddling cited by the Justice Department. But reports this week of wide-ranging questions that the special counsel has prepared for the president himself appeared to bolster complaints from Trump supporters and allies that the probe has metastasized.

“There really are two worlds: There's the population at large who think Mueller's investigation should continue, and Republican primary voters who think it's a witch hunt," said Nick Everhart, a Republican consultant in Ohio, which hosts primaries for key U.S. Senate and gubernatorial races on Tuesday. “Bottom line: Trump's message is not falling on deaf ears. This is a really potent issue and GOP primary voters believe him. "

Over a year into the Mueller investigation, recent polling shows not only an increasing partisan divide in views of the special counsel but also a dip in the general public's thinking about the probe. A Monmouth University poll released Tuesday found that 54 percent of voters support continuing the investigation, down from 60 percent in March. Meanwhile, 43 percent said the investigation should end, compared with 37 percent two months ago. And a Quinnipiac survey last week found that 54 percent of voters believed Mueller was conducting a fair investigation, down four points from March and six points from November.

Similarly, a NPR/PBS/Marist survey in mid-April found 45 percent of voters believe the special counsel is conducting a fair investigation, down three points from March and eight from February. The poll also found unfavorable views of Mueller increasing from March to April among Republicans as well as independent voters, by 19 points and nine points, respectively. Only 16 percent of Republicans view Mueller favorably, as do 35 percent of independents.

"The American people have shown a lack of tolerance for ever-lasting, on-going investigations. And if the '90s are any guide, it bleeds past partisan lines," said Republican strategist Josh Holmes, referring to the independent counsel investigation into then-President Bill Clinton.

And for Republican voters, "the investigation is omnipresent in their world," Holmes said, noting the saturation of coverage by the media and the president's prolific tweets on the subject. "That's the center of the motivation for conservative primary voters. ... They feel like the fix is in."

In Indiana, Rep. Todd Rokita sees the Mueller probe as a way to gain an edge over his Republican rivals Rep. Luke Messer and businessman Mike Braun in their party's U.S. Senate primary on Tuesday. Rokita (pictured) introduced a resolution on Thursday pushing for Mueller's investigation to be shut down if the special counsel does not provide evidence of Russian collusion with Trump associates within 30 days.

"For many Americans, this investigation looks more like an attempt by the Washington elite to destroy President Trump with innuendo, leaks, and baseless allegations than to provide justice," said Rokita. The congressman also released an ad this week centered on the special counsel. "They’re using Fake News to destroy our president,” the narrator says. “Who’s tough enough to stop the witch hunt?" In a debate last month, all three candidates agreed that the investigation should come to a conclusion soon.

GOP candidates in West Virginia's Senate primary, which also takes place Tuesday, have expressed similar sentiments. "It’s a witch hunt," said Attorney General Patrick Morrisey during last week's debate.

"I have seen the witch hunt that has gone after this administration," said Rep. Evan Jenkins. "The Democrats can’t give up on the results of 2016. They’re fighting this administration each and every day."

And former mining executive Don Blankenship, who served jail time for his role in a disaster that killed 29 people, accused the Department of Justice of being dishonest. "It’s one of those things where when you know what really goes on in the Department of Justice, you wonder where this country is going," he said.

The president's disparagement of the DOJ, to which the special counsel reports, might also be having an impact on voters. The April NPR/PBS/Marist survey, for example, found that while 61 percent said the FBI was acting fairly, that number marked a 10-point dip since February. Put another way: 31 percent say the FBI is biased compared to 23 percent who shared that view three months ago. The numbers are even starker among Republicans, 56 percent of whom say the FBI is biased, up 16 points since February, according to the analysis from NPR.

"GOP voters absolutely believe the president is getting wronged, and they trust him more," said Everhart, the Ohio consultant. "He's convinced them what he is saying is happening."

Even Republican candidates who aren't facing primary challenges argue that the Mueller investigation has reached its sell-by date. "I am concerned that this is dragging on and on," Missouri Attorney General Josh Hawley, who is running against Democratic Sen. Claire McCaskill, told reporters on Thursday. "He needs to come forward with the evidence he has -- evidence that I expect will exonerate the president, based on everything we’ve seen. But look, let’s have it. He needs to get on with it here. It is taxpayers who are paying for this."

Meanwhile, polling shows an increase in Democrats' positive views of Mueller and confidence in the probe, and outside groups are fundraising off petitions to protect the special counsel. But party strategists caution against making the Russia investigation a focal point of their campaigns.

"It is sad and frightening that the president is flouting the legal process like this, but for Democrats, we can't make this election about Donald Trump's trial," Hillary Clinton’s 2016 campaign manager, Robby Mook, said on CNN. "Fixating on Russia and this investigation isn't a winning message. We've got to stay focused on drive our own message."

While the probe appears to be having an impact on primary voters, whether and how the investigation, if continued, will shape the electorate in November remains to be seen.

"The more important question is if or how this affects turnout in swing states, like Nevada, which has critically important races coming up this November," said Nevada Republican consultant Robert Uithoven. "Does the endless pursuit of this matter help fuel an intensity gap that benefits Democrats, or does it backfire and motivate Trump supporters to turn out in a midterm that they may have otherwise slept through?"

James Arkin contributed to this report