The billionaire Michael Bloomberg will spend $80m to help Democratic candidates in the midterm elections, US media reported on Tuesday, a significant infusion of cash for a party that has recently struggled with fundraising as it seeks to win control of Congress.

The reported donations came as Donald Trump announced on Tuesday he intended to spend a total of $400m to aid Republican candidates, with $300m already disbursed.

The New York Times reports that Bloomberg made the contributions in September and October, and is particularly focused on Democrats running to flip the US House of Representatives, which Republicans currently control by a historically small margin. The goal, Bloomberg’s political adviser Howard Wolfson told the Times, is to ensure that a Democratic majority is greater than just the 218 seats needed to win control of the chamber.

“The difference between 221 and 230, in terms of the House majority, really matters,” Wolfson said.

One of the world’s richest men, Bloomberg, 84, served three terms as mayor of New York City, from 2002 to 2013. He was an independent then, but later registered as a Democrat, spending $80m to help the party in the 2018 midterms, during Trump’s first term, then made a well-funded but unsuccessful bid for the party’s presidential nomination in 2020.

Among his donations this year are $24m to Everytown for Gun Safety, a group he cofounded that is spending on Democratic candidates in the lower chamber, and $16m to the House Majority Pac, which is connected to the House minority leader, Hakeem Jeffries.

Democrats believe they are favored to take back the House this year, though they’ve acknowledged trailing Republicans in fundraising. Besides Trump’s money, Republicans are being aided by the president’s ally Elon Musk, who has spent $366m on conservative groups and campaigns so far.

Democrats also believe they have a shot at netting the four seats necessary to retake control of the Senate, though analysts believe it could go either way.

Control of either chamber would allow Democrats to block Trump’s legislative agenda and more effectively investigate his administration. If they win a majority in the Senate, the party’s lawmakers could also reject his nominees for the supreme court and other federal judicial positions.

Bloomberg has donated $2.5m to a Super Pac backing James Talarico, the Democratic candidate in Texas’s US Senate race, as well as a Super Pac backing the re-election campaign of the New York governor, Kathy Hochul, and the campaigns of several Democratic gubernatorial candidates, the Times reported.

Asked how effective Bloomberg believed the money would be, Wolfson said: “He is of the view that resources matter in campaigns.” He added that the billionaire “expects a result”.