Former Democratic Senator Jim Webb announces White House campaign
U.S. Senator Jim Webb talks to reporters during his news conference at the U.S. embassy in Yangon, April 11, 2012. REUTERS/Soe Zeya Tun

Former U.S. Senator Jim Webb announced on Thursday he would make a bid for the White House in 2016, becoming the fifth Democrat to challenge frontrunner Hillary Clinton on what is expected to be her march to the nomination.

Webb, 69, who represented Virginia in the U.S. Senate from 2007 to 2012, formed a presidential exploratory committee in November and called for more "positive, visionary leadership" in the United States.

He said in an announcement on his website, JimWebb'16, that he made the decision to run "after many months of thought, deliberation and discussion."

"I understand the odds, particularly in today's political climate where fair debate is so often drowned out by huge sums of money," Webb said.

Webb, a decorated war hero who served in the Vietnam War, is known for his outspoken critiques of U.S. foreign policy and military strategy, and his support for American troops serving overseas.

He has said national defense, criminal justice reform and economic issues that benefit the middle class will be the focuses of his presidential campaign.