Special prosecutor Robert Mueller, tasked with investigating links between the Trump campaign and Russian interference in the 2016 election, has filed charges against 13 Russian nationals, as his investigation continues.

A federal grand jury indicted the suspects last week. Mueller alleges in the charges that the individuals communicated with unwitting members of the Trump Campaign, with the goal of enhancing Donald Trump’s electoral chances and damaging those of his defeated opponent, Hilary Clinton. Notably, the indictment stopped short of any allegation or suggestion that members of the Trump campaign had actively colluded with any of the charged individuals. This is not to say that Mueller will not indict an American in the future, but for now he has steered clear of what would be a watershed moment, charging a domestic citizen.

The charges began back in 2014, and continued in the run up to the 2016 election, which Trump won in a shock victory by a margin of a few hundred thousand votes across four states. This is relevant in a political context, because it raises question marks over the validity of a result which suffered from a direct attempt at foreign interference. For many Democrats, proof of Russian involvement is only the secondary goal to proving the former’s success. In other words, did the involvement of third party forces flip enough votes to have changed the election result?

Though it will be nearly impossible to prove this suspicion, it is likely to be a political hot button issue as the 2018 midterms approach. The President has been increasingly open in his criticism of the Mueller investigation, as well as the wider role of the Federal Bureau of Investigation, even laying the blame for the failure of the Florida regional office to follow up on a tip off about Florida shooter Nikolas Cruz on the distraction and resources allocated to the Russia probe. Tweets have come in thick and fast and Trump seeks to prove his innocence and shift attention to the various scandals that plagued the ill-fated Clinton campaign.

It is plausible that Trump’s concern comes from the likely question of Jared Kushner, his son-in-law and senior political advisor. Kushner has been accused of brokering a meeting with a person claiming to represent the Kremlin, and wishing to supply damaging information on Hilary Clinton. These indictments also suggest that Mueller is treating Russian interference as an electoral law issue, and investigations will focus on those potential breaches.

Additionally, Mueller is seeking to establish whether Trump or those around him deliberately sought out damaging information on Clinton from foreign agents. If this were to be proved, a constitutional crisis would beckon. For the first time in almost two decades, the whispers of impeachment can be heard.