Walker entered the race just three months ago as a top-tier candidate who promised to bridge the divide between the establishment and Tea Party wings of the GOP. But he has steadily lost altitude in both national and early-state polls ever since — and a lackluster performance at the second debate last week put a punctuation mark on his bid.

A CNN poll released today demonstrated the extent of Walker’s collapse: He registers support from less than one-half of 1% of voters nationwide. And his backing traced a similar decline in Iowa, where his campaign has been banking on a strong showing.

“I believe the voters want to be for something, not against someone,” Walker said in brief comments announcing his decision Monday evening in Madison, Wisc.

Walker went on to say he is exiting in the interest of helping “clear the field” for an alternative to Donald Trump. “I encourage other Republican presidential candidates to consider doing the same so the voters can focus on a limited number of candidates who can offer a positive, conservative alternative to the current frontrunner,” he said.

Walker becomes the second presidential candidate to quit the contest, after former Texas Gov. Rick Perry dropped out earlier this month.