HARRISBURG - No, he won't.

That is the answer state Senate Majority Leader Dominic Pileggi gave supporters Monday in announcing that he will not seek the GOP nomination to challenge Democratic U.S. Sen. Bob Casey next year.

"After a great deal of careful consideration, I have decided not to enter the race for the United States Senate," Pileggi, of Delaware County, posted Monday morning on Facebook (www.facebook.com/SenatorPileggi) and Twitter (@SenatorPileggi).

He added: "I will continue to focus on my service as Senate Majority Leader, working for positive change in state government. I thank those who encouraged me to run, and everyone who has offered kind words of support."

He did not elaborate and declined to comment later.

Last week, Pileggi - who would have been the candidate with the highest profile in a crowded Republican field - said he was considering running for the nomination. Again, he made his interest known on social media. He wrote that he had been approached by "a number of people" and was weighing his options.

Pileggi, 53, former mayor of Chester, was elected to the Senate in 2002 and was named majority leader by his colleagues in 2006.

Had he decided to take the plunge, he would have been one of many candidates elbowing one another for the nomination - although political observers say he would have been well-positioned to compete, despite being one of the party's more moderate voices at a time of a conservative surge.

As it stands now, running for the GOP nomination are: former State Rep. Sam Rohrer of Berks County; entrepreneur Steve Welch; Tom Smith, a former coal-company owner from southwestern Pennsylvania; Tim Burns, who built a pharmaceutical-software company and was the GOP nominee for Congress in the 12th District, centered in Johnstown; Marc Scaringi, a Harrisburg-area lawyer and former Senate aide; David Christian, a Bucks County veterans' advocate; Laureen Cummings, a Scranton-area tea-party activist; Bedford County pharmacist John Kensinger; John Vernon, a retired Army colonel from Tioga County; and retired Army Sgt. Robert Allen Mansfield.

Contact staff writer Angela Couloumbis at 717-787-5934, acouloumbis@phillynews.com, or @AngelasInk on Twitter.