Republican networks with more resources to take on Trump have not yet moved to do so. The Koch brothers’ network of donors, though mulling whether to throw support behind one candidate, does not appear poised to actively oppose anyone in particular. Despite the continuing evidence of Trump’s strength, many donors within the network still believe his campaign will eventually collapse.

And even if there were to be any organized effort to take on Trump from outside the official campaign framework, there is no model for what that would look like. The most likely first steps would be donors pooling money for focus groups and polling, to test what messages might work against Trump.

For now, little is happening, adding to the confusion and concern among establishment Republicans. And if attacks were to be employed, there is little certainty that voters would move away from supporting the “outsider” candidates who have surged in this election cycle.

The bottom line for now is that, without donors or outside groups lining up to take down Trump, the onus is on the candidates to do so themselves — or not.