With only 15 days until the election, the nonpartisan Cook Political Report shifted Pennsylvania’s American Senate race from “leans Democrat” to “toss up,” in the latest setback for Democrats seeking to retain their narrow Senate majority. 

Pennsylvania’s three-term incumbent senator, Bob Casey, is seeking his fourth term against a Republican challenger, Dave McCormick, who unsuccessfully ran against Mehmet Oz in the state’s 2022 Republican primary. With the Pennsylvania Senate race shifting, it joins three other races that Cook rates as “toss ups” — in Wisconsin, Michigan, and Ohio. 

“This is big,” the White House press secretary for President George W. Bush, Ari Fleischer, wrote on X of the race shifting.“For a long term incumbent to be in a toss up, something big is happening in PA.”

The shift to “toss up” comes as Mr. McCormick has been making up ground in his public polling numbers and as both parties’ internal polling shows that the Pennsylvania Senate race is a “margin-of-error race,” the Cook Report notes.

RealClear’s polling averages indicate that overall, Mr. Casey is leading the Republican by 1.9 percentage points, a smaller margin than before.

Democrats, seeking to defend 23 Senate seats this election, now face tough odds when it comes to retaining their 51-49 majority, with four toss-up races and with Montana’s Republican challenger, Tim Sheey, forecasted to pick up Democratic Senator Tester’s seat. Republicans, meanwhile, are defending 11 seats that Cook predicts will stay Republican. 

Mr. Casey, like several other vulnerable Democratic senators this election season, ran a new ad recently highlighting similarities with President Trump and distancing himself from President Biden. In the ad, a married couple of split-party affiliation says that Mr. Casey is an “independent” candidate who unites them. They say that Mr. Casey “bucked Biden to protect fracking and he sided with Trump to end NAFTA and put tariffs on China to stop them from cheating.”

The Trump campaign bashed the ad as a desperate attempt by the Democrat to “embrace President Trump” despite Mr. Casey standing for “Kamala’s deranged, radical left agenda.”

Pennsylvania has been a crucial battleground state in the presidential race as well, and RealClear’s polling averages indicate that President Trump is leading Vice President Harris by slightly less than 1 percentage point. 

An analysis by Cook’s Senate and governors editor, Jessica Taylor, notes that internal polling shows that the Pennsylvania Senate race is a “margin-of-error race” and that Mr. Casey holds a “slim, statistically insignificant lead” over Mr. McCormick.

“Though many of the fundamentals may still very slightly favor Casey, this race is now close enough that it belongs more in the Toss Up column than in Lean Democrat alongside Arizona and Nevada, which have clearly become tougher lifts for the GOP,” she wrote. 

The Sun has reached out to both campaigns for comment.