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WASHINGTON — The campaign arm of House Democrats has posted its highest off-year August fundraising haul ever, the group told NBC News.

While their Republican counterparts haven't yet released their August results, the Democratic Congressional Campaign Committee (DCCC) has outraised Republicans each of the three previous months — a result Democrats say bodes well for their prospects of winning the House in the 2018 midterm elections.

"With the House in play, another record-breaking month of fundraising for the DCCC is a clear sign that the grassroots energy behind House Democrats is constantly growing stronger," said Tyler Law, a spokesman for the committee. "Given Speaker [Paul] Ryan's failure to govern with unified Republican control of Washington, it's understandable that vulnerable House Republicans are opting for retirement while we are recruiting incredible candidates deep into the map."

Rep. Nancy Pelosi of California is the Democratic leader and would be in line to return as speaker if Democrats could win back the House.

The DCCC raised $6.26 million in August, compared to $4.15 million for August 2015, the last comparable year before a midterm election. Overall, the DCCC has raised $72.46 million in 2017. And the committee touted its online fundraising, which it says has totaled $31.26 million for the year so far, including $2.4 million last month.

While lagging a bit in recent months, the National Republican Congressional Committee (NRCC) still had a sizable $12 million cash-on-hand advantage over Democrats as of July, and both parties had raised about the same amount for the year. Ryan, R-Wis., buttressed the committee's fundraising last month with a $2 million cash infusion.

Notably, House Democrats' financial success comes as the Democrat National Committee has struggled with its own fundraising.