The champagne was flowing as hedge fund executive Robert Mercer and his daughter Rebekah hosted a reception during the Cannes Film Festival last May to promote "Clinton Cash," a film by their political adviser Stephen K. Bannon and the production company they co-founded, Glittering Steel. The Mercers, Republican mega-donors who had spent millions on the failed presidential bid of Sen. Ted Cruz of Texas, and Bannon, then executive chairman of Breitbart News Network, were still weeks from formally aligning with Donald Trump's campaign. But the festivities that balmy evening aboard the Sea Owl, the Mercers' luxurious yacht, marked the growing influence of their financial and political partnership in shaping the 2016 campaign - and in encouraging the populist surge now reverberating around the world. The Mercers' approach is far different from that of other big donors. While better-known players such as the Koch brothers on the right and George Soros on the left focus on mobilizing activists and voters, the Mercers have exerted pressure on the political system by helping erect an alternative media ecosystem, whose storylines dominated the 2016 race. Their alliance with Bannon provided fuel for the narrative that drove Trump's victory: that dangerous immigrants are ruining the country and corrupt power brokers are sabotaging Washington. The wealthy New York family and the former investment banker-turned-media executive collaborated on at least five ventures between 2011 and 2016, according to a Washington Post review of public filings and multiple people familiar with their relationship. The extent of their partnership has not previously been reported. Through those projects, the Mercers and Bannon, now chief White House strategist, quietly built a power base aimed at sowing distrust of big government and eroding the dominance of the major news media. The Mercers provided the money, while Bannon, working in tandem with Rebekah, acted as business partner and political guide. The family's overarching strategy, according to people familiar with their giving, is to test various tactics to see which is most effective. "The Mercers have a Silicon Valley approach to politics: Let a thousand entities bloom, and let's see what works," said one associate, who, like others close to the Mercers, spoke on the condition of anonymity to discuss the private family. The Mercers poured money into Breitbart News, the media outlet they now partly own that under Bannon's leadership gave voice to the nationalistic fervor Trump embraced. The family helped finance an investigative think tank that Bannon co-founded, the Government Accountability Institute, whose president wrote "Clinton Cash." Glittering Steel, the Mercer film production company, then brought the book's findings to the screen, portraying Democratic presidential candidate Hillary Clinton to a mass audience as a captive of wealthy interests. The alliance continued with Cambridge Analytica, a data science company that did work for the Trump campaign, with the Mercers as investors and Bannon on the board. And they joined forces on a nonprofit watchdog group that is putting the spotlight on how public money is spent in the Mercers' home state of New York. While other donors gave more to support Trump's presidential bid last year, the Mercers are now arguably the most influential financiers of the Trump era. Bannon, who went on to manage the final months of Trump's campaign before joining the White House, is the senior architect of the president's policy vision. He is joined in the West Wing by counselor Kellyanne Conway, a friend of Rebekah Mercer who led the family-funded super PAC that backed first Cruz and then Trump in the 2016 race. People who know them say the Mercers, who soured on traditional political operatives, appreciated Bannon's business savvy and share his belief that the conversation around politics must be changed for their ideas to prevail. For all of their power and privilege, both the family and their longtime adviser see themselves as outsiders, fighting the grip of elite institutions. Driving the Mercers is a belief "that there is too cozy a relationship between the established media and the political class, and that there needs to be more accountability," said Peter Schweizer, president of the Government Accountability Institute and author of "Clinton Cash." "They loathe the fact that Washington has become a very wealthy town because of government power, at the expense of the American people." The Mercers declined to comment. Bannon declined to comment through a White House spokeswoman. Trump himself paid homage to the family in December, weeks before moving into the White House, when he attended the Mercers' elaborate annual costume party at their Long Island mansion. In a nod to the "Villains and Heroes" theme, Rebekah Mercer dressed like the Black Widow and her father as Mandrake the Magician, a comic-book superhero known for hypnotizing his targets. Trump - who did not wear a costume - told the crowd that when the famously taciturn Robert Mercer urged him to hire Bannon and Conway last August, he knew he should listen because Mercer so rarely speaks, according to people in attendance. Just a decade ago, few could have predicted the Mercers' swift ascent in the money world. In the 2006 midterms, the family contributed only $37,800 to federal candidates and political committees - including $4,200 that Robert Mercer's wife, Diana, gave to Clinton's Senate reelection campaign, federal records show. The family's foundation was similarly low key, giving away $292,000 in 2007, with nearly half going to a nonprofit math foundation started by one of Robert Mercer's hedge fund colleagues, tax documents show.

But, after the election of Barack Obama, the family started to increase its political giving, tapping into newfound wealth. In 2010, Robert Mercer was elevated to co-chief executive of the hedge fund Renaissance Technologies, whose closely held quantitative formulas have generated staggering returns. The following year, he began drawing annual earnings of $100 million and up, according to Institutional Investor's Alpha list. Meanwhile, the Supreme Court's Citizens United decision in 2010 paved the way for new forms of unlimited political spending - an opening seized upon by mega-donors on the right opposed to the Obama administration. Between 2008 and 2016, they pumped at least $77 million in political donations and gifts from their family foundation into a vast universe of causes across the conservative landscape, according to campaign finance reports and tax filings. Their foundation financed groups focused on international affairs, religious freedom, state policies, judicial issues and free enterprise. They poured millions into the Koch network and super PACs that promoted Republican candidates across the country. Much of the Mercers' political spending came in 2016 alone, when they funded a family super PAC with $15.5 million, including $2 million to support Trump once he secured the GOP nomination, according to Federal Election Commission filings. The Mercers' ideology resembles that of many conservative donors and opinion leaders. They believe in limited government and free markets, according to people who know them. They both have a staunch antipathy to the Clintons. Rebekah Mercer, who home-schools her four children, is strongly antiabortion, associates said. But what sets the Mercers apart is their interest in finding new ways to shape the environment in which policy issues are debated, an impulse driven by their background in technology and finance. Robert Mercer is a renowned computer programmer who helped pioneer the field of machine translation. He made his fortune after leaving IBM for the hedge fund Renaissance Technologies in the early 1990s.He bought an estate with a harbor view on Long Island and a 203-foot yacht, which includes flourishes such as a four-deck-high tree carved from Peruvian mahogany and a rosewood self-playing Steinway baby grand piano. Rebekah Mercer, 43, a former Wall Street trader, lives with her family in a sprawling triplex in a Trump-branded condominium on Manhattan's Upper West Side and sits on the boards of the American Museum of Natural History and the Heritage Foundation. She and her two sisters also run an online gourmet cookie company. She is the most political of Mercer's three daughters, largely directing where the family puts its resources, and is known in conservative circles for her unyielding and skeptical questioning of candidates and established political operatives. "They are right-wing nerds," said George Gilder, an economist and former Ronald Reagan adviser who met Robert Mercer when the hedge fund executive began attending speeches Gilder has given touting bitcoin and a return to the gold standard. "[Robert Mercer] believes in free markets, and he believes that technology is a positive force and that a lot of government is overregulating and suppressing economic creativity," Gilder added. Andrew Harnik / AP From left, President Donald Trump's chief of staff Reince Priebus, Vice President Mike Pence, and Trump's senior adviser Steve Bannon attend a joint news conference with Trump and German Chancellor Angela Merkel in the East Room of the White House on March 17, 2017. From left, President Donald Trump's chief of staff Reince Priebus, Vice President Mike Pence, and Trump's senior adviser Steve Bannon attend a joint news conference with Trump and German Chancellor Angela Merkel in the East Room of the White House on March 17, 2017. (Andrew Harnik / AP) (Andrew Harnik / AP) One of the biggest beneficiaries of the Mercers' donations over the past eight years has been the conservative watchdog Media Research Center, which collected $13.5 million from the Mercer Family Foundation between 2008 and 2014, tax records show. The center's projects include a website called CNSNews.com that publishes stories it says are ignored by the mainstream media - an early precursor to Breitbart News. L. Brent Bozell III, founder of the Media Research Center, did not return requests for comment. But in an interview with The Post last year, he called the family "visionaries" when it comes to recognizing new ways to communicate with the public. "What they are looking to do is build a movement, not just fund a movement," Bozell said. "I don't know where it is all leading, but I can tell you they are in it for the long haul." The Mercers' partnership with Bannon began in 2011, thanks to an encounter that Robert and Rebekah had with Andrew Breitbart. During a spring meeting of Club for Growth donors at the Ritz Carlton in Palm Beach, Florida, the Mercers sought out Breitbart after watching him deliver a talk about how to co-opt the political strategies used by liberals. The conservative media entrepreneur, who liked to denounce the mainstream press as the Democrats' "dominant partner in crime," was arguing at the time that government policies could not be changed until conservatives seized control of the media narrative. The message resonated with the Mercers, according to a person familiar with their views. Breitbart introduced them to Bannon, then a screenwriter and producer in Southern California who was directing a movie called "Occupy Unmasked" that featured Breitbart. It was co-produced by the conservative advocacy group Citizens United, whose allied foundation would later receive Mercer funds. Bannon, whose peripatetic career had taken him from Wall Street to Hollywood, was at the time increasing his political focus, directing and producing a slate of conservative documentaries. He had grown close to Breitbart and was urging the writer to expand his website, which originally operated out of Breitbart's basement. As part of that effort, the Mercers invested $10 million in the enterprise in the summer of 2011, according to a person familiar with the transaction. When Breitbart died of a heart attack the following March, Bannon became executive chairman of the news outlet. The Mercers' co-ownership of Breitbart News, along with chief executive Larry Solov and Breitbart's widow, Susannah, was confirmed by the company last month. Breitbart News Network, the far-right media outlet that heralded President Donald Trump's rise and was once led by his top White House strategist, is owned in part by a wealthy conservative family that poured millions into propelling Trump into office, the company's chief executive acknowledged... The site was an early champion of Trump and the anti-establishment, populist movement that buoyed his campaign. It has also fielded intense criticism for airing inflammatory stories about immigrants, refugees and radical Islamists. Bannon once touted it as a "platform" for the alt-right, a small, far-right movement that seeks a whites-only state and whose adherents have espoused racist, anti-Semitic and sexist points of view. Breitbart officials have disputed charges that their content promotes racism or Islamophobia. Solov did not respond to requests for comment.