 -- Former Maryland Gov. Martin O'Malley suspended his campaign for President tonight, thanking Americans for "giving me an opportunity to be a part of writing this story of our country's future."

"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.

Early on, many pundits believed O’Malley would eventually hit a break and emerge as the progressive alternative to Hillary Clinton. He tried to emphasize his youth, executive experience, and depth of knowledge on the issues, but nothing seemed to resonate with voters.

In many ways, O’Malley’s platform mirrored Bernie Sanders', with a focus on taking on big money in politics and enacting Wall Street reform.

But unlike Sanders, O’Malley had a Super PAC and did not come across as authentic and passionate as Sanders did with progressive voters.

The riots and racial unrest that exploded in O'Malley's city of Baltimore just weeks before he announced his presidential bid also seriously hampered his run and put his executive credentials into question. Protesters with the Black Lives Matter movement disrupted his campaign launch in Baltimore and several other events throughout his campaign.

O’Malley did receive accolades from Latino voters for his comprehensive immigration reform ideas and progressive promises to offer asylum and refugee to unaccompanied minors and others fleeing violence in Central America. He drew big applause lines on the trail when he compared Republican frontrunner Donald Trump’s language to fascism.

“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."