The nationwide midterm elections will take place in four days, and the focus on candidate quality for Republicans in key Senate races remains a factor. However, recent shifts in polling seemingly reveal concerns from voters about the quality of several Democratic candidates.

During a luncheon in August, Senate Minority Leader Mitch McConnell cited "candidate quality" as a reason why he believes Republicans will face difficulty in flipping the Senate in November and instead might only be able to flip control of the House.

Since McConnell's prediction, several Senate races have tightened, with some of the Republicans he appeared concerned about holding narrow leads over their Democratic challengers as issues like crime, inflation and immigration come into focus ahead of Election Day.

While concern about GOP candidate quality may have faded in terms of polling, some believe Democratic candidates are viewed unfavorably because of positions they have taken on issues that voters care about most.

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Catherine Cortez Masto, John Fetterman, Raphael Warnock, Mandela Barnes

Democratic Senate candidates from left to right: Nevada Sen. Catherine Cortez Masto, Pennsylvania Lt. Gov. John Fetterman, Georgia Sen. Raphael Warnock, and Wisconsin Lt. Gov. Mandela Barnes. (Kriston Jae Bethel/AFP, Elijah Nouvelage, Anna Moneymaker, Daniel Boczarski via Getty Images)

Erin Perrine, vice president of Tag Strategies, told Fox News Digital that a "candidate's views are directly tied to their electability" and that "Democrats in New York, Wisconsin and Pennsylvania nominated extreme candidates who were untouched in the primary process."

"Once voters saw how extreme and out-of-touch candidates like [Kathy] Hochul for governor, and [Mandela] Barnes and [John] Fetterman for Senate are on crime, rising costs, and energy, the races became much more favorable for Republicans," Perrine said. "And in the current climate, candidates Democrats put forth to run in swing states and deep blue states alike may prove to be too extreme to be palatable by the electorate."

In Pennsylvania, Democratic Senate candidate John Fetterman's lead over his Republican challenger, Mehmet Oz, has shrunk following his rocky debate performance last month.

A USA Today/Suffolk University poll following the Oct. 25 debate showed that Fetterman maintains a slight edge over Oz, 47%-45%, well within the margin of error. An earlier poll in September reported Fetterman with a six point lead over Oz, 46%-40%.

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"Senate Democrats are rolling into an election with a historically unpopular president and no answers to a tumultuous economy, inflation at the highest point in decades, and food, housing, and gas prices through the roof," Rachel Bovard, senior director of policy for the Conservative Partnership Institute, told Fox. "That, more than anything, is determinative of where they may end up electorally."

Bovard insisted that "candidate quality is a big factor in compelling voter trust" and that a lot of the Democrats "have no accomplishments to run on."

"Candidate quality is a big factor in compelling voter trust," she said. "And when you have candidates like John Fetterman, who is struggling to recover from a stroke and unable to handle the rigors of the campaign trail, and even incumbents like Raphael Warnock and Mark Kelly who have no accomplishments to run on, it's that much harder of a sell. Because politics is about policy, yes, but it's also about connecting to voters in a visceral way and convincing them you can be trusted with their interests. Democrats are just out to sea on both."

Similarly, in Georgia, incumbent Democrat Sen. Raphael Warnock's lead over his GOP opponent, former Heisman winner Herschel Walker — who has been plagued with allegations of promoting quack COVID-19 cures and accusations of paying for two abortions — has dwindled in polling in the Peach State.

Herschel Walker debated Raphael Warnock

Georgia GOP Senate candidate Herschel Walker and Democratic Sen. Raphael Warnock. (Getty Images)

The latest Fox News survey of Georgia registered voters, released Wednesday, shows the two candidates in a dead heat, with Warnock up by just 1 point over Walker, 44% to 43%. In September, the Democrat was up by 5 percentage points; in July, he held a 4-point lead.

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The contest shifts in Walker’s favor when focusing exclusively on people saying they have already voted or are certain to vote: 45% Warnock, 46% Walker. In September, it was 47-43% Warnock.

Despite the rise in polling from Republicans, some believe that Democrats are on cue with messaging and that their quality is not of utmost concern headed into the elections.

Jessica Tarlov, a Democratic strategist and co-host of Fox News' "The Five," said she does not believe Democrats are "running bad candidates" in the midterms, however.

"No one could've predicted Fetterman would have a stroke and would be well ahead if people didn't have reservations about his health," she told Fox. "Warnock and Kelly are very strong, and my expectation is that they can win their races. When it comes to Mandela Barnes, it was clear that he was vulnerable on crime — which is Ron Johnson's major emphasis — but I wouldn't call him a weak candidate like a Walker or Masters."

"I believe the tide is turning against Democrats because of the general climate, not because of their quality," Tarlov added.

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The Wisconsin Senate race between incumbent GOP Sen. Ron Johnson and his Democratic challenger, Wisconsin Lt. Gov. Mandela Barnes, has also tightened, with most polls marking it as a toss up race.

A Fox News survey of Wisconsin voters, released earlier this week, showed Barnes trailing Johnson by three percentage points (45%-48%), within the poll's margin of error. That is mostly unchanged from last month, while it was Barnes who was ahead by four points in August.

johnson and barnes at wisconsin senate debate

A Fox News survey of Wisconsin voters released this week showed Mandela Barnes trailing Ron Johnson by three percentage points (45%-48%). (AP Photo/Morry Gash)

Similarly, a Marquette University Law School poll of 679 likely Wisconsin voters found Johnson edging Barnes within its margin of error. Approximately 50% of likely voters in that survey said they support Johnson in the race, compared to 48% for Barnes.

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Much of the same could be said about the Nevada Senate race, which pits incumbent Democrat Sen. Catherine Cortez Masto against former state Attorney General Adam Laxalt, a Republican.

A Suffolk University/USA Today poll, which was conducted Oct. 24-28 among likely voters, showed Cortez Masto with a slight edge over Laxalt 45%-44%, within the margin of error. The incumbent’s one-point advantage is essentially unchanged from her 46%-44% advantage over Laxalt in the pollster’s previous survey, which was conducted in early October.

Democratic Sen. Cortez Masto and GOP challenger Laxalt

Sen. Catherine Cortez Masto, left, and Republican challenger Adam Laxalt, right, are running in a dead heat race in Nevada. (Associated Press)

Laura Fink, founder and CEO of Rebelle Communications, said she believes Cortez Masto is "connecting with Latino small business owners and working class voters in Nevada by talking about how to lower the cost of living there."

An average of recent polls in the Nevada Senate race compiled by Real Clear Politics indicates a contest that is essentially a tie.

"Democratic candidates are even in the polls even with gale force political winds in their face," Fink said. "The quality of Democratic candidates has enabled them to defy the traditional midterm disadvantage of the party in power, economic headwinds and a sour presidential approval rating to beat the odds. Republicans should be dominating — but they aren't — because not only are their candidates that bad but because swing state Democrats are that good."

"The quality of Democratic candidates has made what should be a referendum on the party in power into a choice election — because they have done a better job winning voters trust," Fink added.

Incumbent Arizona Democratic Sen. Mark Kelly's lead over his GOP challenger, Blake Masters, has also shrunk.

A Fox News poll of Arizona registered voters, released Tuesday, showed Kelly with a 2-point edge over Masters (47% to 45%), which is within the poll's margin of error.

Mark Kelly and Blake Masters

A Fox News poll of Arizona registered voters shows Sen. Mark Kelly with a 2-point edge over Blake Masters (47% to 45%), which is within the poll's margin of error. (Dimitrios Kambouris/Brandon Bell)

The race has tightened since August and September when Kelly was up 8 and 6 points, respectively.

The Ohio Senate race between Democratic Rep. Tim Ryan and Republican JD Vance has also tightened up, with recent polls signaling the race is much closer than it once was.

A recent Marist Poll shows Vance with support from 46% of registered voters compared to 45% for Ryan, who has attempted to portray himself as a moderate in the race. Among voters who said they are definitely going to vote in the midterm elections, the race is even closer, with both candidates tied at 47%.

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Democrats currently hold a razor-thin majority in the Senate with 50 seats in their party's control. Democrats only need 50 seats to retain power because Vice President Kamala Harris can cast a tie-breaking vote.

The Senate remains a toss-up. Fox News' Power Rankings show 47 seats going to the Democrats and 49 to the Republicans.

Fox News' Victoria Balaria, Greg Wehner, Paul Steinhauser, Ronn Blitzer, and Timothy H.J. Nerozzi contributed to this article.