WASHINGTON — Rep. Tammy Duckworth, D-Ill., is raising money for a 2016 U.S. Senate bid, telling supporters in letters obtained by the Chicago Sun-Times she knows in her “gut” she can win. The latest fundraising appeals are the firmest signs yet that Duckworth, a wounded Iraq war vet, is very close to announcing her entry into the Senate contest.

On Monday evening, Duckworth will gather some of her top donors at a home in the Hancock Center to discuss securing the Democratic nomination to run against Sen. Mark Kirk, R-Ill., who is seeking a second term.

In the letter to her best fundraisers about the Hancock meeting, they were told “contributions are encouraged but not required. We realize it is early in the election cycle, but we are asking our top supporters to consider a donation. The maximum an individual can give before March is $5,400. If Tammy decides to not to run for Senate, we will offer you a refund. If she does run, this support will be key in keeping up with Senator Kirk’s $2 million and counting campaign war-chest.”

And in another letter, seeking $1,000 donations, she urged a contribution “if you believe I should be a candidate for the Senate in 2016.” Once she gets in a race against Kirk, Duckworth said, “in an instant I’ll become a lighting rod for the right and all the special interest money they can pour in the race. My gut tells me I can beat these guys.”

Duckworth, 47, from Hoffman Estates, who represents the 8th Congressional District, anchored in the northwest suburbs, was elected to her second House term in November. Last month, she returned to work after taking a maternity leave for the birth of her daughter, Abigail.

Three other U.S. House Democrats from Illinois are considering a run: Rep. Bill Foster, Rep. Robin Kelly and Rep. Cheri Bustos. Even if none of the four House Democrats gets in the 2016 Senate race, just raising the potential of a run is an effective fundraising tool.

Former Rep. Joe Walsh, R-Ill., a radio talk-show host, said he is considering challenging Kirk in a GOP primary.