Hedge-fund magnate Robert Mercer now tops the list of the biggest donors of 2016, with more than $17 million in contributions to super PACs, according to a Washington Post analysis. (Andrew Toth/Getty Images)

A burst of giving by liberal donors and a last-ditch effort to fend off GOP presidential front-runner Donald Trump helped super PACs pick up nearly $100 million in new donations by the end of March, pushing the total raised by such groups this cycle to more than $700 million, according to a Washington Post analysis of Federal Election Commission reports.

At this pace, super PACs will raise $1 billion by the end of June. In the entire 2012 cycle, such groups brought in $853 million, according to FEC filings.

The Post is keeping a running tally of the largest contributors of the 2016 cycle, whose six- and seven-figure checks have allowed super PACs to spend $278 million so far on ads and voter outreach.

Already, nine mega-donors have each given at least $10 million to such groups, which can take unlimited sums from individuals and corporations. Together, that tiny cadre has provided 17 percent of the money raised through March 31, The Post found.

Now topping the list of mega-donors: conservative hedge-fund magnate Robert Mercer. His total giving reached $17.2 million after he put $2 million more into a super PAC supporting Sen. Ted Cruz (Tex.) in March. The Renaissance Technologies co-chief-executive moves up from fourth place, bumping liberal San Francisco environmentalist Tom Steyer out of the No. 1 slot.

A look at the donors giving record sums this cycle.

Another Renaissance Technologies figure joins the top 10 list this month: James Simons, an elite mathematician who founded the hedge-fund giant. Together, he and his wife, Marilyn, have given $10.13 million to super PACs this cycle, the vast majority to Democratic groups. The bulk of James Simons’s donations — $7 million — have gone to Priorities USA Action, a super PAC backing former secretary of state Hillary Clinton.

Other wealthy Democrats allied with Clinton stepped up their contributions significantly in March, making Priorities the top-raising super PAC for the month. The group, which plans to unleash a $91 million TV ad blitz in support of Clinton in June, brought in nearly $12 million in March.

Meanwhile, a surge of investment in the Stop Trump movement drove a slew of donations by rich conservatives. Among the big givers: hedge-fund co-founder Cliff Asness, who made it onto The Post’s top 50 list after shelling out $1 million in March to Our Principles, an anti-Trump PAC. Investor Michael Vlock, who is married to billionaire Karen Pritzker, gave the group $1.7 million in the same period.

For the first time, a publicly traded corporation cracked the top 50 list: oil giant Chevron, which has given $3 million to GOP congressional super PACs.

The Chevron money reflects an uptick in funds flowing to super PACs on both sides of the aisle that are focused on House and Senate races. The GOP Senate Leadership Fund brought in $2.95 million in March, while the Democratic Senate Majority PAC took in $2.49 million — the best fundraising month both groups have had so far this cycle. Their coffers are expected to expand significantly as donors in both parties turn their attention to congressional races that now may be in play because of Trump’s volatile candidacy.

Big money is seeping into individual congressional races in new forms, with a proliferation of super PACs created to support a single candidate each. One such group, Maryland USA, which has backed the House bid of Republican national security expert Amie Hoeber, is financed almost entirely by her husband, Mark Epstein, a senior vice president at Qualcomm. Epstein poured $2.1 million into the group, making him one of the 50 biggest givers of 2016.

In April, Hoeber won the GOP primary with 29 percent of the vote. She will face off against Democratic Rep. John Delaney in November.