Michael Bloomberg, the billionaire former mayor of New York City, plowed $43 million into super PACs supporting Democrats in the first two weeks of October, a sign of his intensifying political influence in the final stretch of the midterms as he secures his place among the top three donors this election.

Bloomberg, who previously had declared himself a political independent and this month announced he has registered as a Democrat, divided the $43 million between his super PAC Independence USA and the Senate Majority PAC, which works to elect Democrats to the Senate, Federal Election Commission records filed Thursday night show.

Bloomberg is weighing a potential 2020 presidential bid and has pledged up to $100 million in support of Democrats this cycle, saying he was frustrated with inaction in Congress under Republican leadership and that a divided government would be more effective in legislating.

The Fix’s Amber Phillips breaks down the five Senate races most likely to flip parties ahead of the 2018 midterm elections. (JM Rieger/The Washington Post)

His latest giving brings his total contributions this cycle to at least $57 million, and he is expected to inject more cash through Election Day.

This week, Independence USA reported ad buys for the final stretch of the campaign in two of the most competitive House races: $4.5 million in support of Katie Hill, the challenger in California’s 25th Congressional District, and another $4 million boosting the Democratic challenger Harley Rouda against incumbent GOP Rep. Dana Rohrabacher in California’s 48th Congressional District.

The super PAC has also supported various Democratic candidates in Washington, Virginia and Michigan.

“Mike Bloomberg has always believed we all have a responsibility to do what we can to help the country. . . . We need a change of direction in Washington, and we need to elect leaders who will reach across the aisle to start solving problems — and start uniting our country instead of dividing it,” a Bloomberg spokesman said in a statement.

The new campaign finance disclosures also showed big fundraising hauls for Senate Democratic incumbents in the first 17 days of October.

Sen. Heidi Heitkamp (D-N.D.), one of the most vulnerable Senate Democrats this fall, saw a spike in fundraising in early October — a boost that coincided with her key vote against Brett M. Kavanaugh, President Trump’s Supreme Court pick, a risky move given that she is trailing her Republican opponent in a state that Trump won by 36 points.

Heitkamp raised $12.6 million in the first 17 days of October — making up 46 percent of her total fundraising haul this cycle. Sixty percent of the donations she received in this period came from contributions of $200 or less, which could be a sign of grass-roots support from Democratic supporters following her Kavanaugh vote.

In contrast, Heitkamp’s opponent, GOP Rep. Kevin Cramer, raised $630,000 in the first 17 days of October, with $976,000 in campaign cash. Heitkamp had $11 million in cash as of Oct. 17, filings show.

In the Missouri Senate race, Democratic incumbent Claire McCaskill raised $4.7 million in the first two-and-a-half weeks of October, compared to the $1.7 million raised by her GOP challenger Josh Hawley. About 40 percent of McCaskill’s haul from Oct. 1 through Oct. 17 came in smaller donations of $200 or less, compared to 24 percent for Hawley.