Fox News Digital Politics editor Chris Stirewalt was asked about key midterm election races to watch Monday on "The Daily Briefing."

Ahead of New Jersey's Tuesday primary, Dana Perino asked Stirewalt what could be expected in the left-leaning state's 2018 U.S. Senate race, with its incumbent, Robert Menendez (D).

"Could it be possible that a Republican named Bob Hugin could take on Bob Menendez -- the incumbent -- and win?" Perino asked. 

Stirewalt said that there is no hard evidence to show the longtime Capitol Hill fixture Menendez is in any electoral trouble, but noted that the 64-year-old's brush with federal prosecutors may or may not have an effect on voters' opinions.

Judge Nap: SCOTUS Ruling in Same-Sex Wedding Cake Case Is 'Dangerous'

NJ Gov. Murphy Reinstitutes Statewide ObamaCare Individual Mandate

Prosecutors dropped bribery and fraud charges against Menendez and his alleged actions in connection with his longtime friend and donor Dr. Salomon Melgen, a Florida ophthalmologist, after lengthy court proceedings led to a mistrial.

However, Menendez was "severely admonished" by the Senate Ethics Committee in April.

"In most states, coming within a hair's breadth of the federal prosecutors as incumbent Senator Bob Menendez did, and the things Bob Menendez admitted that he did -- yeah, he beat the rap," Stirewalt said.

Stirewalt said Hugin, a businessman from Menendez' hometown of Union City, is largely self-funding his campaign and therefore not requiring much in the way of financial support from the national party in an otherwise blue state.

"If Menendez is as unpopular as some people think he is, this could be a race," Stirewalt said.

He said that observers should take note of how well Menendez fares in his Democratic primary election Tuesday, to see how many Democrats choose someone other than the senator.

The latest Quinnipiac Poll -- from March -- shows Menendez with a 17-point lead over Hugin going into November's general election.

'There's No Standard for the Left': Bongino Says Joy Reid Is Getting 'Free Pass' for Blog Posts

Huckabee: 'Please, God, Let Nancy Pelosi Continue to Be the Voice of the Democratic Party'