A poll from the Democratic bastion of New Jersey finds President Trump leading by a point and the Republican nominee for Senate, Curtis Bashaw, within striking distance. The national parties have long overlooked the Garden State. This year, it’s emerging as a potential decider for Washington’s balance of power.

A survey by co/Efficient found President Trump leading President Biden among New Jersey’s likely voters 41 percent to 40 percent. Seven percent favored a third-party candidate — Democrats are suing to keep the independent, Robert F. Kennedy Jr., off the ballot — and 13 percent were undecided, with a 3.42 point margin of error.

The poll was conducted on June 26 and June 27. That means before Mr. Biden’s collapse in the presidential debate. That will have Democrats watching future surveys with dread. It’s unlikely they can lose a key brick in their Blue Wall and go on to retain the Senate, not to mention the White House.

Defending New Jersey against Mr. Bashaw and Trump — who held a massive rally in Wildwood and owns a golf club in Bedminster — won’t be cheap for the Democrats. The state is sandwiched between the number-one media market, New York, and the fourth, Philadelphia. Ben Franklin, no dummy, called it “a keg tapped at both ends.”

Four years ago, Mr. Biden carried the Garden State by 16 percent. Now, his job approval is 20 points underwater, 56 percent to 36 percent. President Trump is much closer to the surface, with 45 percent approving and 50 percent disapproving.

New Jersey’s electoral votes haven’t gone to a Republican since President George H.W. Bush in 1988. Yet in the co/Efficient survey’s generic ballot, Republicans drew 39 percent compared to 42 percent for Democrats, a statistical dead heat. 

The Senate drought for New Jersey Republicans runs back to 1972, when they last won a seat. This year, they hope a favorable environment — and an unconventional Republican in Mr. Bashaw — give them the best chance in generations to reverse their fortunes.

Also breaking against Democrats is the fact that their incumbent, Senator Robert Menendez, is running as an independent. After failing to win his renomination due to indictments on charges ranging from obstruction of justice to bribery, he lost the primary to Congressman Andrew Kim.

Head-to-head, Mr. Kim leads Mr. Bashaw by seven points, 41 to 34 percent. The addition of Mr. Menendez drew two points from Mr. Kim and one from Mr. Bashaw, reducing the margin to six. Mr. Bashaw, a political newcomer building name recognition, is happy to see his race so competitive.

Last month, Mr. Bashaw told the Sun that Democrats can’t “put me in a box.” He’s a “married, gay man” and “lifelong Republican,” who beat a Trump-endorsed candidate in the primary. He did so, he said, by winning “the hearts and minds of New Jerseyans,” who in the co/Efficient poll listed inflation, taxes, and the border as their top three concerns.

“Democrats,” Mr. Bashaw told me via email, “have failed to deliver anything for New Jersey families except for corruption, higher taxes, inflation, and chaos at the border. You can’t keep electing the same career Democrat politicians and expect different results.”

“As a political outsider and a businessman,” Mr. Bashaw said, “I know how to get things done, and I’ll work to fix inflation, secure our border, and protect New Jersey families.” It’s canny framing to meet the moment. The poll found 25 percent of voters are undecided in his race, and conventional wisdom holds that that cohort breaks for a challenger on Election Day.

Republicans also draw hope from the 2021 gubernatorial race, which featured a strong showing by a former assemblyman, Jack Ciattarelli. In a contest that the incumbent Democrat, Governor Murphy, was expected to win in a walk, Mr. Ciattarelli came within 3.2 percent — about 84,000 votes — of an upset.

“As Maine goes, so goes the nation” was a maxim when, between 1820 and 1932, the party that won the state’s governorship matched that of the White House victor. This year, New Jersey may be the new bellwether, with thirsty Republicans hoping to drink from the Garden State keg and, once again, get a taste of glory.