White House press secretary Sean Spicer briefs reporters at the White House on Monday. (Jabin Botsford/The Washington Post)

What qualifies as collusion? It's a question that could eventually become important, whenever special counsel Robert S. Mueller III and congressional committees wrap up their investigations of Russian interference in the 2016 presidential race.

Suppose investigators were to determine that aides to President Trump's campaign did not participate in Russian hacking or disinformation schemes but were aware of the efforts. Would that make the Trump campaign guilty of colluding with the Kremlin?

The White House surely would argue no, if it were to come to that. But such an argument would be harder to make, after remarks on Monday by Trump and his spokesman, Sean Spicer.

Here's what the president said on Twitter:

Trump was reacting to a Washington Post report about Obama's response, in the months leading up to Election Day, to CIA intelligence showing that Russian President Vladimir Putin had ordered a cyber campaign aimed at disrupting the U.S. presidential race. Trump seemed to be suggesting that Obama's failure to stop further interference — Democratic National Committee emails already had been hacked and leaked at that point — was tantamount to collusion with Russia.

This would be a classic Trump turnaround: I colluded? No, you colluded!

It also would be a remarkably tough standard: knowledge plus inaction equals collusion. It is not hard to see how such a standard could come back to haunt Trump, if investigators were to conclude that even one of his aides knew what Russia was up to and didn't blow the whistle.

To protect Trump from being held to this standard, Spicer could have attempted to clean up the president's mess during Monday's press briefing. He could have argued that Trump meant Obama colluded with the Clinton campaign by holding off on sanctions against Russia that might have been viewed as politically-motivated attempts to help his chosen successor.

Instead, Spicer reinforced the idea that not stopping Russia is the same as colluding with Russia. Witness this exchange with a reporter:

Q: Can you clarify what he meant in his tweet? He accused former president Obama of colluding or obstructing. What evidence does he have?

Spicer: I think — again, what I will just leave it at is that clearly they, according to this report, knew back in August. If they were so concerned, why didn't they stop it? What did they do?

Q: Well, the report is very extensive. It goes into all of those details — that they were blocked in a number of different measures; that they were concerned about looking like they were intervening in the election on behalf of Hillary Clinton. President Obama did talk to President Putin —

Spicer: Well, they seemed to throw —

Q: So what evidence does he have that President Obama was colluding or obstructing?

Spicer: Well, again, I think it comes back to this idea that they've been very clear, they've been playing this card about blaming Trump and Russia. And yet, at the same time, they were the ones who, according to this report, knew about it and didn't take any action.

So the question is, were they — if they didn't take any action, does that make them complicit? I think that there is a lot of questions that have to get answered about who didn't know what and when.

If it turns out that Trump aides knew absolutely nothing about Russian meddling, then Spicer's suggestion that the Obama administration was “complicit” won't hurt the White House at all. But if someone on Trump's team was even vaguely aware of Russian disruption, Spicer will have hamstrung the White House's defense.