INDIAN WELLS, Calif. — The political network overseen by industrialist billionaires Charles and David Koch on Saturday pledged to spend nearly $400 million on the midterm elections to defend Republican majorities in Congress and in state legislatures across the country.

The Koch network, meeting for its annual winter donor conference near Palm Springs, Calif., said the investment would also focus on promoting conservative policies and was equal to a 60 percent increase over what it spent in the 2016 presidential election. The campaign was set to include a $20 million expenditure to promote the Republican tax overhaul passed and signed into law late last year.

"We're all in," Tim Phillips, president of Americans for Prosperity, told reporters during a news conference to kick off the conference at the Renaissance Esmeralda Indian Wells Resort and Spa.

Phillips conceded that the political environment for Republicans is "challenging," though he declined to pin the blame on President Trump and his low job approval ratings and instead credited the toxic atmosphere for the GOP to historical trends that have seen the party in control of the White House lose seats in most midterms.

"Presidents in their first off-year election, it's always a struggle," Phillips said, when pressed on whether Trump was making the November elections particularly difficult for his party. "I'm not downplaying the challenge ... We acknowledge that the left is energized."

The Koch network billed this weekend's conference as it's biggest ever in its 15-year history: 550 attendees total, including 160 first-time attendees, among them hundreds of Republican campaign donors who participate in with the Koch brothers' political groups.

Also Saturday, the Koch network, whose policies are clearly conservative but lean libertarian, lauded Trump for the framework he introduced to provide legal status to the "Dreamers," illegal immigrants brought to the U.S. as young children by their parents through no fault of their own.

“Immigrants are essential to the success of our country and addressing the plight of the dreamers is a top priority for this Network. We are committed to working with Congress and the White House to find a solution that does this without arbitrarily reducing the number of people who come here to contribute,” Brian Hooks, co-chairman of Koch's Seminar Network, said in a statement.

The Koch group was pleased to see Trump put legalization on the table for the full population of Dreamers. But it is concerned about the parts of the president's framework that propose reducing legal immigration significantly and possibly abolish "chain migration," also known as "family reunification."

“We applaud the president for taking this important step towards a bipartisan compromise that delivers enhanced security for our nation and permanent legal status for 1.8 million Dreamers, ensuring they have the legal certainty to plan their lives and increase their contributions to America," Daniel Garza, president of the Koch group, The LIBRE Initiative, said in a statement.

"That said, we cannot support arbitrary cuts to future legal immigration levels. We welcome a debate about whether our current legal immigration policy properly balances family and skills-based migration. But that broad debate should not distract from the immediate goal of providing certainty to Dreamers and enhancing security," Garza added.

Editor's note: The story has been changed to more accurately reflect the wider scope of Koch network's fundraising pledge for the 2018 midterms beyond just helping Republicans.