Mercer didn’t get involved in conservative philanthropy until 2010, when he became one of the first large donors to take advantage of the Citizens United decision that allowed for unrestricted corporate funding of political candidates.  However, his real entrée into the brash movement conservatism of the political right came a year later when he met Andrew Breitbart of Breitbart News, and then Steve Bannon, and Pat Caddell, Jimmy Carter’s former pollster, who, like Bannon, had strong ties to Trump.

Mercer quickly became Breitbart’s biggest booster.  The foundation’s funding allowed the magazine to hire a large full-time staff and to become a font for Alt-Right propaganda on everything from radical Jihadism and illegal immigration to political correctness in academia and the mainstream media.  Mercer’s funding of the Media Research Center, which dwarfs Scaife’s, also allowed MRC to vastly expand its operations and reach.

Mercer appears to have played an important role in promoting Trump’s candidacy, even though like many conservatives, he was skeptical at first that the former reality star had the “temperament” to become president — and initially gravitated toward Ted Cruz.  However, according to two separate investigative reports – one by Jane Mayer at The New Yorker, another by two Washington Post reporters – Mercer was eventually persuaded to support Trump, in part due to the intervention of his influential daughter Rebekah, who’s been described by some as the conservative right’s “Iron Lady.”

Rebekah, unlike her father, who’s often described as socially awkward, is an outspoken firebrand much like Trump, with whom she’s developed a close relationship.  She was even named to the White House transition team.

The full extent of the Mercers’ funding to right-wing causes over the past five years is unknown.  However, according to Mayer’s report, Mercer gave $11 million to the Media Research Center between 2011 and 2014 alone (about three times the $4 million Scaife provided over a longer period) and $2 million to Citizens United in 2012.  In addition, Mercer has provided a whopping $25 million in funding to the Koch Brothers in recent years to support their own conservative funding priorities (The Kochs routinely deny their sources of funding).

As of 2015, the Mercers were doling out $24.5 million annually, about 35% higher in value than Scaife’s most recent project portfolio.

The biggest difference between the two funders may be their underlying ethos and preferred operating methods.  Scaife’s funding is still titled toward established think-tanks and policy groups – not just Heritage but other conservative stalwarts like the American Enterprise Institute — that wage a more traditional “war of ideas.”  The Mercers tend to support the new breed of more aggressive agit-prop rebels of the Alt-Right.

David Horowitz of the eponymously named Freedom Center, who is a Scaife grantee ($5.5 million) and also a Bradley Foundation grantee ($6 million since the Center’s founding, including nearly $4 million since 2001)  but is also close to the Mercers, draws a distinction between “think-tanks” and “battle-tanks.”  While there is clear crossover in their funding, Scaife tilts more toward the former, the Mercers more toward the latter.

In addition to some overlap in their funding projects, The Mercers and Scaife share some interlocking memberships.  Officers of the Scaife Foundation and the Mercers are leading members of the Council on National Policy, which brings together a few hundred of the most important conservative donors with key right-wing operatives for thrice-annual meetings to discuss movement strategy.

Rebekah Mercer has also joined the board of the Heritage Foundation. More cross-over board memberships of this kind are likely to appear in the future.

The fact that Scaife and Mercer — representing two very different eras of right-wing philanthropy — have converged around Trump is a clear indication of just how unified “movement” conservatives have become in their overall agenda — despite some latent disagreements on specific policy issues.

And yet few conservatives seem to know whether the unpredictable Trump can be counted on to implement their full agenda — or if, like Reagan, they will be fighting constant and often disappointing battles to keep their new standard-bearer from “straying” once — with their indefatigable support — he’s firmly ensconced in the White House.