Washington (CNN) A major outside group intended to serve as the political muscle behind Donald Trump's nascent presidency is sputtering and potentially splintering as tension tears the nonprofit further from its biggest donor, multiple sources close to the group told CNN.

America First Policies, a group set up this winter to advocate for the Trump agenda, is treading water at best at a time when other, rival groups are staffing up and pushing them toward the sidelines. If the nonprofit does not regain its footing, several Trump allies fear that it could find itself out-punched politically as several looming policy battles invite a raft of spending from Democratic interest groups.

One group source, granted anonymity to candidly assess the nonprofit's launch, conceded that "it has been slow."

A month after a splashy group of senior Trump advisers promised "significant" funding, the group has barely lifted a finger to politically bolster the young administration. And as a pricey fight beckons this month over the future of the Supreme Court, the president remains unpopular and seems almost certain to not have the "surround-sound super structure" that the White House once envisioned.

Much of the drama stems from an ongoing dispute with the Mercers, a father-daughter set of donors who have become intertwined deeply within the Trump political infrastructure. The Mercers were initially expected to provide much of the funding for the group.

Bob and Rebekah Mercer are known for being exceedingly controlling of how their dollars will be spent, but it remains disputed how much sway they will hold over the nonprofit, according to three people briefed on the discussions. Several of the Mercers' most trusted hands went to work in the West Wing, leaving the nonprofit largely run by a half-dozen aides loyal to either Vice President Mike Pence or to Jared Kushner, Trump's son-in-law.

Part of the dispute, according to one of the people, centers on whether the Mercers will have a seat on the nonprofit's board of directors. The placement would require a $1 million contribution, the person said, a buy-in that sources described them as uneasy about handing over.

"I don't get the sense that they're driving the train with this group," said one person close to the organization. "This is not a personality-driven entity. That shell game has come and gone."

The Mercers did not respond to a request for comment on their support for the group, nor did Brad Parscale, who is in charge of the nonprofit. The Mercers, people familiar with the relationship say, harbor particular dislike for Parscale, who was Trump's top digital strategist and is close with Kushner.

Now, several strategists involved are considering working with multiple rival nonprofits simultaneously, according to a group source, which would be unusual and raise questions about which group they are serving at any given time. The Mercers may choose to form their own group, and it is unclear whether Home Depot founder Bernie Marcus — the other mega-donor expected to provide substantial backing to the group — may go with them. A Marcus aide declined to comment.

"There's a healthy dose of desire to do different things," said the group source, who said the Mercers' involvement was "still to be determined."

America First Policies is one of at least three nonprofit groups trying to assert itself as a major player in the new political order — it is set to release its first advertising spot this week as inquires swirl about its future. The groups can accept checks of unlimited sizes and shield their donors' identities as long as most of the money is focused on policy, not elections.

It's a new challenge for Trump big-money supporters: How can a group support an incumbent president who is far more likely to drive the conversation than their ads might?

"Americans seem to trust their friends and communities more than their leaders," said Ken McKay, who led a pro-Trump super PAC during the campaign that disbanded after the election and who is no longer involved with the outside groups.

"Maintaining and building support horizontally is more important than ever, and those groups can help with that."

But the groups are only as powerful as their donors -- and in a twist of irony, some of the likeliest Republican givers are off the board for Trump organizations since Trump named them to his Cabinet. Some of the most reliable Republican givers during the campaign, from Commerce Secretary Wilbur Ross to Small Business Administration chief Linda McMahon, are settling into their new Washington bureaucracies, not cutting seven-figure checks to big-money groups.

Another hurdle: Several group leaders have cited Organizing for America, Barack Obama's nonprofit, as a model. Yet OFA, which was born directly out of Obama's reelection campaign, did encounter the same crowded, disputed terrain that awaits the host of Trump nonprofits. Unlike the Democratic group — which clearly had the imprimatur of the president — each of the Republican groups claims some mantle of legitimacy from the administration, even though none of their arguments are convincing enough to dry up the fundraising reserves of the others.

That clutter is a remnant and reminder of the general election, when a half-dozen super PACs rose and fell at various points as Trump campaign aides did. No Super PAC ever secured a durable "blessing" from the Republican nominee, and high-wattage donors scattered across different groups, many of which were underfunded and disorganized until the very last weeks of the campaign.

But today there is little downside for Republican donors -- and some Democrats, even -- to financially support the leader of the GOP for at least the next four years.

The pool of likely donors has deepened.

But while some anti-Trump donors have sought to make amends, a minority has cast their aspersions on the entire party and treated Trump as an infection. Michael Vlock, a longtime GOP financier who grew disgusted by Trump during the primary, recently told the National Republican Senatorial Committee that he wasn't interested when asked if he'd like to speak by phone with new NRSC chair, Sen. Cory Gardner.

"I will no longer support any Republican until and unless they repudiate Trump. The party has been co-opted or has surrendered to the ignorant and dishonest sociopath presumably because, in spite of his policies that are at odds with numerous fundamental conservative principles, they believe that they can achieve much needed legislative changes by holding its nose and accepting him," Vlock wrote in an email to the NRSC aide, which he shared with CNN.

"Until and unless they repudiate Trump," he continued, "every Republican will find, deservedly, that their legacy is irrevocably stained."

Because nonprofits do not have to disclose fundraising hauls or contributors, it's unclear just how alone Vlock may find himself. A survey of major conservative givers during the 2016 campaign revealed few who had committed major contributions to the nonprofit, with Republican contributors ranging from Warren Stephens to T. Boone Pickens telling CNN they had no contact with America First Policies.

Meanwhile, rival groups are trying to fill the sudden void. Great America Alliance, one such nonprofit, revealed to CNN that this week will announce a $1 million advertising campaign in 2018 Senate states portraying Trump as a promise-keeper. It boasts Trump confidants Rudy GIuliani and Newt Gingrich as chairs.

"The difference between us and other organizations is that we have principals," claimed Eric Beach, the group's strategist.

And one group with a track record of success is run to the wealthy Ricketts family of the Midwest. Future 45, a super PAC which thanks to a half-dozen of the most elite Republican donors spent close to $30 million on Trump's behalf, and its linked nonprofit has hired a suite of A-list Republican operatives from around Washington as it prepares advertising campaigns on Trump administration priorities.

In addition to the money left over from the campaign — a substantial majority of which came from Las Vegas casino titan Sheldon Adelson — the groups are actively fundraising, throwing it into competition with other pro-Trump groups that is all too familiar.