Former Maryland Gov. Martin O’Malley has spent the last year supporting candidates in down-ballot races across the country. Wearing blue jeans and rolled-up sleeves, he’s proselytized to volunteers and local party leaders — in places like in Lower Gwynedd, Pa., Waukesha County, Wis., and Thermopolis, Wyo. — that the best way for Democrats to change the direction of the country is to win back the states.

Of course, it’s easy to view Mr. O’Malley’s march on the states as merely attempt to get back on the road to the White House. Funded by his political action committee and aptly named Win Back Your State, his initiative certainly provides a reason to campaign around the country, build relationships in local political circles, expand fundraising outreach and earn some free national media coverage. Trips to early primary states — for example, headlining events for local candidates in Cornish, N.H., and in Linn County, Iowa, — along with affable redirects when asked specifically about a 2020 presidential run reinforces a more cynical interpretation of his advocacy on behalf of others.

But party-building and Marty-building are not mutually exclusive endeavors — and the presence of presidential ambitions doesn’t negate the short-term necessity and potential long-term benefits of a focus on the states for the Democratic Party.

Indeed, while the election of Donald Trump and a Republican majority in Congress was a disaster for Democrats in 2016, it’s the continued GOP dominance in the states that is their more pervasive problem.

After heavy losses in 2008, Republicans — bolstered by anti-Obama sentiment among their rank-and-file and the tea party movement — focused resources on winning state-level elections. The goal was to produce state governments with Republican-majorities that would eventually determine how the district lines would be drawn post-2010 Census. In total, Republicans gained around 1,000 state legislative seats in the 2010 and 2014 cycles, and the redistricting — that some have likened to gerrymandering on steroids — which resulted from their successes has hindered the ability of Democrats to recoup their legislative losses.

Republicans now hold majorities in both chambers in 31 state legislatures. Democrats control just 14. The remaining legislatures split control between them. The partisan make-up of the states, in contrast, was essentially reversed a decade ago.

Party control of a state legislature comes with power that is often underappreciated by the average voter. The majority party sets the policy agenda for the state, while the minority party is left with procedural maneuvers, amendments and often futile appeals for bipartisan cooperation. A governor can either enhance or check the power of a legislative majority — and the GOP has been has been similarly successful in electing state-level executives over the same time period.

The states are a political training ground, thus the last few election cycles have also kept Democratic talent from the field. Those fresh-faced, politically unknown local candidates that Mr. O’Malley is stumping for today might be the congressional and presidential candidates of the future. To this point, nearly half the current members of Congress and more than half of all U.S. presidents and vice presidents once served in their state legislatures.

Like Mr. O’Malley, Democratic leaders, donors, and activists recognize what’s at stake for them as a new redistricting process looms in 2020. Since President Trump took office a year and a half ago, Democrats have managed to flip 43 state legislative seats — some in heavily Republican districts — and are contesting more legislative seats now than they have in the past two decades.

Experts contend that the current political environment will likely put more Republican chambers at risk during the current election cycle. But in order to make substantial gains in the states — like Republicans did in 2010 — Democrats need to strategically identify districts and promote candidates on whom voters can focus their motivation.

To his credit, that’s precisely what Martin O’Malley has been doing. And there is perhaps no better messenger for the advantages of unified party government and determining district lines than him.

Mileah Kromer is the director of the Sarah T. Hughes Field Politics Center at Goucher College, which conducts the Goucher Poll. She is also an associate professor of political science. Her email is mileah.kromer@goucher.edu; Twitter: @mileahkromer.