O’Malley was poised to fly to Iowa, the nation’s first presidential nominating state, after a 10 a.m. announcement at Federal Hill Park in Baltimore, the city where he lives. He will visit New Hampshire on Sunday.

Building support in those states is crucial to his upstart strategy. Despite multiple trips over the past two years, O’Malley remains largely unknown to voters and registers in the low single digits in polls.

He is banking, boosters say, on the prospect that Clinton’s widespread support will crater as more voters assess the baggage she brings to the race and that O’Malley — a two-term governor with string of progressive accomplishments — will emerge as the most credible alternative.