Martin O'Malley Suspends Presidential Campaign

O'Malley was polling behind Bernie Sanders and Hillary Clinton.

"I want to thank everyone who came out to our events and lent me their ear and everyone who went out to caucus for me tonight," O'Malley said.

"Words cannot express how grateful I am to all of you my true friends who have helped me in waging this courageous battle," he said. "When I got into this 8 months ago I had no doubt that it would be anything but a tough fight. And it is a tough fight. But I have always been drawn to a tough fight."

Campaign sources told ABC News that "O'Malley spent more time in Iowa than any other candidate and remained the most accessible."

"He ran an energetic and honorable campaign - leading the field with the most bold progressive policy proposals, and he successfully pushed the other candidates on gun safety, immigration, and climate policy," the sources said.

During the eight months of his candidacy, O’Malley was never able to find his own lane within the Democratic race and stayed in single digits nationally and in Iowa.

“Trump says we should be monitoring everyone of the Muslim faith ... Let me ask you this. Who is next? Catholics? Trade unionists? Artists? We've seen this road before, and it does not lead to a good place,” O’Malley told a crowd of Democrats in New Hampshire in June. “Panic and political opportunism are a toxic mix -- a mix that can often precede fascism or the plunging of our republic into a security state."