Trey Radel, the Florida freshman congressman charged with cocaine possession last November, returned to the Capitol after a stint in rehab only to learn that he'd picked up a primary challenger. Paige Kreegel, a former member of the Florida State House, formally launched a campaign to unseat Radel Tuesday.

Radel invited journalists into his congressional office to apologize for his actions and refocus his attention on his duties as a Member of Congress, although he would not divulge whether he would seek re-election this fall.

"I cannot express how sorry I am. I ask for your forgiveness. I've let down our entire country. I have let down my colleagues on both sides of the aisle, and I've let down my family," Radel said contritely. "Re-election is the absolute last thing on my mind. The most important thing right now is my health, my family and getting back to finding solutions and getting something done."

Late last year, Radel was the target of an undercover sting operation when he was busted for possession of cocaine. He pleaded guilty in a Washington, D.C. Superior Court and was placed on one year's probation with "minimal supervision."

Watch: Congressman Trey Radel Busted for Cocaine

Tuesday Radel pledged to "work hard every single day" to rebuild trust with his constituents, congressional colleagues and family. He said he has not yet spoken to House Speaker John Boehner since leaving a Florida rehab facility on Dec. 19, although he said he had an appointment to meet with the speaker this week.

"From here, I've built a support system, for the rest of my life, to carry me through this," he said. "I will do that to deal with this very personal issue, and now I'm hoping to deal with the issues that face our country. And in doing so I will do it one day at a time."

Radel conceded that his battle with alcoholism will persist "for the rest of my life," but said he was still receiving out-patient treatment as he works to overcome his addictions.

"There's a group that exists that works on a 12-step process that is based in anonymity and literally millions of people around the world depend on that anonymity," Radel said. "I have a support system that is voluntary, I have a support system that I have specifically chosen to use as well and I have colleagues and friends who have been tremendously helpful."

Without explicitly mentioning Radel's ethics or legal troubles, Kreegel, who lost to Radel in the 2012 primary, contends that the constituents of Florida's 19th District deserve "serious, sober representation."

"Southwest Florida should expect a congressman who can lead, a congressman without distractions, a congressman they can trust," Kreegel said in a statement announcing his candidacy. "The partisan bickering, frat boy house-style leadership and divisive rhetoric in Washington has become an embarrassment, and southwest Floridians deserve better."

Watch: Trey Radel Pleads Guilty to Cocaine Possession

Kreegel, a medical doctor by trade who served in the state legislature from 2004 to 2012, said his medical experience made him "uniquely qualified to address" the issues with the new health care law.

"The politicians in Washington had their chance with health care reform, now it's time to bring in a doctor that will hold them accountable and help cure this disaster," Kreegel stated. "I will focus on common-sense solutions that are based on conservative principles and conservative values."

Kreegel may not be the only challenger hoping to oust Radel. State Senate Majority Leader Lizbeth Benacquisto is considered a likely candidate, and former Rep. Connie Mack - Radel's predecessor - is also believed to be considering a bid to win back the seat.

The House Ethics Committee established an investigative subcommittee Dec. 16 to determine whether Radel's criminal actions violated the Code of Official Conduct or any law, rule, regulation or other applicable standard of conduct in the performance of his duties or the discharge of his responsibilities. If he is found guilty of the alleged violations, he could face three possible courses of action - expulsion, which is unlikely, or censure or reprimand.