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The GOP’s most dependable sugar daddies might be putting away the checkbook.

In January 2015, the Koch brothers were eagerly sharing their plan to drop nearly $1 billion on the 2016 cycle and other political endeavors in support of conservative candidates and causes. Less than 18 months later, insiders within the pair’s vast political network are concerned that the Kochs may be shutting off the financial spigot entirely.

On Monday, National Review published a lengthy account of changes in how the Kochs plan to invest their considerable fortune—changes that conservatives fear signals an end to their lavish spending on federal elections.

The Koch brothers have been cast as oligarchical villains for their obscene spending, a characterization that has damaged both their personal and corporate brands, according to National Review. And considering the limited return on their investments in the last presidential election, exactly how much influence their dollars wield was in doubt.