Florida Sen. Bob Graham announced Monday that he would not seek re-election to a fourth term in the U.S. Senate.

Graham, who ended his bid for the Democratic nomination for president last month, said it was a hard decision to make.

“This has been a very difficult decision for me and my family and I know for some of you it is a disappointment,” Graham said at a news conference at a high school in Tallahassee, where he was conducting one of his “workdays.”

Five Democrats — former USF President Betty Castor, U.S. Reps. Allen Boyd, Peter Deutsch and Alcee Hastings and Miami-Dade mayor Alex Penelas — have been waiting for Graham to make his announcement so they could move on with their campaigns.

Castor said Monday that Graham was Florida’s biggest “cheerleader” and that she will look to him for advice in the coming months of her campaign.

“Bob Graham loves Florida and has worked as hard as anyone in our history to make this state of which we are all proud,” Castor said. “Through his workdays, he interacted with and understood working Floridians and their needs. He championed Florida business and made our university system his passion.

“I will call on Sen. Graham for his wisdom and counsel. As a leader, he leaves big shoes to fill.”

Graham, who turns 67 Sunday, is a former two-term governor and is considered one of the most popular politicians in Florida, where he has served in the Senate since 1987. He delayed his entry into the presidential contest to recover from major heart surgery in January. He later dropped out.

His decision on re-election was kept secret until early Monday.

However, Castor said though she is sad to see Graham leave and wishes him the best of luck, she is ready to move her campaign in full gear.

“Before (Graham) made his announcement, I had been campaigning throughout the state and it has been somewhat difficult to fund raise,” Castor said. “Hopefully, now people will not be as reluctant to give money because they know for sure I am running.”

Castor filed the necessary paperwork in June to run for the U.S. Senate and she added that she has already turned in two quarters of campaign finance reports.

Castor said she will spend more time campaigning in the coming days and months, especially in Hillsborough County.

“I want to build as much name recognition as I can before next August (primary) because winner takes all,” she said.

House Speaker Johnny Byrd, Plant City-R, who is also running for U.S. Senate, sent out a statement Monday about Graham not seeking re-election.

“While Bob Graham and I did not agree on most policy issues, I have always respected his commitment to the people of Florida and his love of public service. I wish him and Adele all the best in this new chapter of their lives,” Byrd said.

Other Republicans seeking the U.S. Senate seat are Larry Klayman, a legal activist, former U.S. Rep. Bill McCollum and state Sen. Dan Webster of the Orlando area.