[Ed. – The case for collusion that never was but which Democratic lawmakers continue to pursue.]
The Papadopoulos “collusion” claims (without collusion charges) are alleged in the Mueller report, which essentially repeats the grandiose “Statement of the Offense” that the special counsel included with the comparatively minor false-statement charge to which Papadopoulos pled guilty. Carefully parsed, this narrative stops short of alleging that the Trump adviser actually collaborated with a Russian agent. Rather, it claims that Papadopoulos engaged in a lot of twaddle with Mifsud, who he had reason to suspect might be a Russian agent. The pair brainstormed endlessly about potential high-level Trump-campaign meetings with the Putin regime, including [insert heavy breathing here] between Trump and Putin themselves. Papadopoulos then exaggerated these meanderings in emails to Trump-campaign superiors he was hot to impress.
It is virtually certain that Mifsud was not a Russian agent. Whether he was an asset for any intelligence service, we cannot say with certainty at this point.