DOVER — Just one incumbent lawmaker lost Tuesday — but the one who did was arguably the most powerful member of the General Assembly.

Sen. Patricia Blevins, the president pro tempore, was defeated by Anthony Delcollo, 50.6 to 49.4 percent.

The upset not only means senators will have to choose a new president pro tem but, coupled with Sen. Bethany Hall-Long’s win in the lieutenant governor’s race, gives the Republican Party a chance to take control of the Senate for the first time since 1973.

The Democratic Party has controlled both chambers of the General Assembly and the governor’s office for the past eight years, and while the governorship is safe for another eight years and the House for at least two, the GOP could strike a major blow by winning next year’s special election.

Patricia M. Blevins

“We believe that balance in state government will improve state government,” Senate Minority Whip Greg Lavelle, R-Sharpley, said Wednesday.

Sen. Hall-Long, a Democrat from the Middletown-area 10th District, could wait to resign as state senator until after new lawmakers are sworn in in January and votes are cast on naming a new president pro tem. Doing so would allow the Democrats to keep control of the Senate for at least a month.

After she resigns, the two sides will be deadlocked at 10-10, although, with the lieutenant governor casting the deciding vote, the Democrats have an edge.

Bethany Hall-Long

The special election would then be scheduled to take place at some point between the middle of February and the beginning of March.

Candidates for the two sides are chosen by members of the respective county parties after hopefuls make their case.

Rep. Earl Jaques, D-Glasgow, has been mentioned as one possible candidate for the Democrats. He could not be reached for comment Wednesday.

Although the 10th District has about 15,600 Democrats to 9,800 Republicans, the GOP could flip it. John Marino garnered 48.9 percent of the vote against Sen. Hall-Long in 2014.

Now facing questions about both the short-term and long-term future of their caucus’ majority, Democratic senators are trying to regroup.

An Elsmere Democrat, Sen. Blevins had served the 7th District, which has twice as many Democrats as Republicans, since 1991. She had been the president pro tem for the past four years.

In a statement, Senate Majority Leader David McBride, D-Wilmington Manor, praised Sen. Blevins and thanked her for her service.

“As is longstanding practice, the longest-serving member of our caucus, Sen. Harris B. McDowell III, will soon call together the Senate Democratic caucus to discuss leadership roles and other issues heading into the 149th General Assembly,” he said. “We will move forward together, united in our commitment to serving our great state as Patti did.”

Republicans were looking to win the Senate Tuesday on the strength of four young candidates all hoping to unseat longtime incumbents, but three of the challengers came up empty. Still, the result left Democrats reeling and gave the GOP a reason for optimism.

Former Gov. and U.S. Rep. Mike Castle, a Republican, said he was pleased Sen.-elect Delcollo won. Going forward, he believes the state GOP needs to strengthen its message.

“I think we Republicans needed to perhaps do a better job of pointing out some of the really good times back a number of years ago where Pete du Pont was governor and I had a chance to be governor” in the 1970s and ‘80s, he said.

Mr. Delcollo could not be reached for comment Tuesday or Wednesday.