WASHINGTON — Democratic candidates are outpacing the fund-raising of their Republican rivals in key congressional races, but huge checks from conservatives assured that their side will remain financially competitive in the weeks before next month’s midterms.

In an election season that appears likely to shatter midterm fund-raising records, Democrats outraised their Republican opponents in 32 of the closest 45 House races by a total margin of $154 million to $108 million since November 2016, according to an analysis of reports filed Monday with the Federal Election Commission. Even in the 13 targeted races in which Republicans outraised their Democratic rivals, the margin was a less gaping $41 million to $31 million.

The breakneck Democratic campaign fund-raising, much of which was fueled by donors giving small sums online, has boosted the confidence of party leaders. They believe the financial advantage will give them the resources they need to harness an enthusiasm gap and capitalize on enmity for President Trump headed into Election Day.

To take the majority in the House of Representatives, Democrats need to flip at least 23 seats currently held by Republicans. For Democrats to win control of the Senate, a more difficult task, they would have to defend 26 seats — including 10 in states won by President Trump in 2016 — and flip two of the five Republican seats considered in play.