Robert Mueller’s Trump-Russia probe is moving full steam ahead.

On Monday, former Trump campaign head Paul Manafort was indicted in relation to the probe. Rick Gates, himself a former campaign official, also surrendered. The indictments themselves were not related to the campaign but to the fact that the two men had not paid taxes for millions of dollars in income.

What’s more, former Trump campaign adviser George Papadopoulos pleaded guilty to lying to the FBI about his interactions with Russian nationals in relation to his attempts to find “dirt” on Hillary Clinton during the election — and the indictments and guilty plea could well be the first step to bigger things for the investigation.

The fact that indictments have been handed down means that an independent grand jury has found probable cause to think a crime did, in fact, take place. Prosecutors only lay charges if there is a good chance that they will be able to secure a conviction, per Department of Justice policy.

It should also be noted that this could be only the first of several indictments. The likelihood that this charge will land directly at Trump’s feet is unlikely, but investigators could be using these charges as a tool to get someone to flip on Trump and the campaign.

Mueller has been investigating whether Trump committed obstruction of justice asking then FBI Director James Comey to drop the Flynn investigation, not to mention the fact that Trump later fired Comey when the investigation was not dropped.

Under DOJ policy, President Trump cannot be charged with a crime while sitting as president; he would have to be impeached. While the law is not clear, the plan may be to seal the indictment now and then unseal it on the day Trump leaves office, whether or not he is impeached.

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Still, at this point, it is unlikely that the president himself will see charges. It is much more likely that someone such as Michael Flynn or Paul Manafort or even Carter Page will face charges.

New Jersey Republican Gov. Chris Christie has weighed in on the matter, saying that anyone involved in Mueller’s Russia probe should be concerned with the indictment news.

“I think anybody who’s been advised by the special counsel’s office that they’re a target of the investigation  which I’m sure he has done to those people who are  should be concerned,” Christie said in interview with Jake Tapper on CNN.

He also stated that the apparent leak in the investigation shows that the credibility of the investigation could be called into question. In the past, Christie has said that Mueller should resign if he has any conflicts of interest though, he now says he sees no reason at this point for Mueller to do so.

“I’ve not yet seen anything that makes me think he must step down, that there’s an absolutely indisputable conflict,” Christie stated before adding, “I think that he has to be very, very careful about making sure that the public believes that he has no conflicts and that his integrity is unquestioned.”