Indian Wells, California (CNN) At a confab in the California desert this weekend, leaders of the powerful political and policy network founded by billionaire benefactors Charles and David Koch issued a stark warning for the midterm elections: President Donald Trump's unpopularity could be churning up a Democratic wave.

"Let's be frank right up front: these elections are going to be brutally tough," Emily Seidel, CEO of the Koch group Americans for Prosperity, told a ballroom filled with hundreds of the network's biggest donors Monday.

AFP President Tim Phillips echoed that dire warning, equating the political landscape this year with that in 2010, a historic wave election that swept Republicans to control of the House, but "with one big difference."

"This year, we're on defense," Phillips said.

Historically, a new president's party faces steep odds in the first midterm election -- but Trump's approval ratings, typically a strong indicator of party performance in an election, are particularly anemic. Those numbers, coupled with low approval for the Republican-led Congress, are "making the environment even more challenging this year," Seidel said.

Meanwhile, elections last year with high Democratic turnout suggest the party is energized leading into the midterms, Seidel said. Democrats have consistently led Republicans on the generic ballot polling during the past year.

John DeBlasio, a Chicago-based donor who was attending the Koch seminar for the first time, noted the President's low approval as a clear "headwind" for Republican candidates.

"So, what do you do?" DeBlasio said. "I think that's going to be a challenge for members in how they accept the President's policies, but distance themselves a little bit from him personally."

Acknowledging these dynamics, the Koch network confirmed this weekend that it plans to spend close to $400 million on political and policy messaging during this election cycle, a new high-water mark for the network in a midterm election.

Their strategy will encompass early media spending in the first half of this year, and further investments in the network's grassroots infrastructure, which now spans 36 states.

AFP has identified 14 key Senate races and is already engaged in four: Wisconsin, Missouri, Indiana and Florida. And 80 competitive races will comprise the House battlefield, they said, including the 23 Republican districts where Hillary Clinton won.

Retirements shaping the map

The House landscape is complicated further for Republicans by a flood of retirements in swing districts, they said. Underscoring the challenge, an audiovisual presentation shown to Koch network donors Monday was already out of date by the time Seidel and Phillips took the stage -- not taking into account the announcement Monday morning by House Appropriations Committee chairman Rodney Frelinghuysen, R-New Jersey, that he will not seek reelection.

That announcement brings the total competitive districts where Republicans are retiring to 16, Phillips said, "and it's only January."

As Koch networks donors convened this weekend for an annual retreat, they marked a glittering year for their political and policy priorities, in which congressional Republicans approved and the president signed into law a sweeping tax reform measure. But a sense of foreboding also hung over the meeting, with network leaders and donors collectively sounding the alarm regarding the coming election cycle.

"This midterm is going to be hard," donor Gail Werner-Robertson told Charles Koch and the rest of the assembled crowd during one session Sunday. "We need everybody to help. We can't lose the progress you have fought so hard for."

Speaking with reporters later Sunday, Art Pope, a prominent North Carolina donor, said he is "very concerned" about the landscape for Republicans in 2018. "Historically, the first election for the President's party, that does not work out favorably for them."

Pope said he believes that Republicans are better positioned this year than Democrats were in 2010, due to strong economic indicators. But the energy among Democratic voters in elections last year nevertheless suggests a challenging environment for Republicans, he added.

"There is absolutely no doubt that the Democrats are motivated," Pope said.

Some pockets of hope among donors

Some donors were more optimistic. Doug Deason, a Texas-based patron, said he believes Republicans will gain seats in the Senate and maintain control of the House.

But, he added, "We're going to have to spend a lot of money."

Leaders of the Koch network confirmed this weekend that they are prepared to do just that. Of the roughly $400 million budgeted for this election cycle, the network plans to spend $20 million selling the new tax law to the public.

However, their reach will have some limits. The network historically has not engaged in party primaries, and Phillips said there are no plans to do so this year. And the network will not give candidates air and ground cover across the map: Notably, the Koch network does not have a presence in California, which is expected to be a key battleground in Democratic efforts to take back the House.

But the network's leaders stressed Monday that they will make a difference where they can, employing a "business-like approach" to the election.

"We've never faced a challenge like this year brings," Seidel told donors Monday. "But we see pathways to success. ... So, folks, let's fight. And let's fight now."