The argument du jour in partisan circles today goes like this: Special counsel Robert Mueller's investigation should end because of the alleged bias of FBI agents who resented candidate Donald Trump. Some conservative lawyers have expanded this argument by claiming that the Russia investigation is the "fruit of the poisonous tree." They are wrong on the law, wrong on the facts, and they should know better.

As former United States attorneys, we have experience prosecuting federal crimes. The Russia investigation had a proper factual and legal foundation, and recent writings are nothing more than an improper effort to wrap inapplicable legal doctrines around discredited fiction to undermine the rule of law. If we are to preserve the bedrock principles of our democracy, we must call out these partisan attacks for what they are, illegitimate and baseless, and let the special counsel conclude his work.

Start with the unsound arguments assembled to end the investigation, based on the "fruit of the poisonous tree" doctrine, which is merely a way for defendants to exclude at trial evidence that was illegally obtained. We have been on the receiving end of defense counsel pitches that an investigation should end for some perceived flaw. Our response is the same: Take it up with the judge. Court is the place to challenge the propriety of any criminal investigation, and only after charges are filed.

In this case, the FBI properly initiated an investigation into Russia's efforts to interfere in the 2016 presidential election, including whether Trump campaign associates were involved. The FBI must adhere to the guidelines for domestic FBI operations that were last updated by former Attorney General Michael Mukasey. The guidelines state that "preliminary investigations may be initiated on the basis of any allegation or information indicative of possible criminal or national security-threatening activity." This includes information indicating that an individual or organization may be a target of attack or recruitment in connection with criminal activity. In order to collect evidence through a wiretap, the FBI must show a federal judge that probable cause exists.

Based on public reporting, which is likely only the tip of the iceberg, there was more than sufficient information indicating possible criminal or national security-threatening activity for the FBI to open an investigation into Russian interference. We would be stunned if, based on these facts, the FBI had not initiated an investigation. Indeed, the Republicans on the House Intelligence Committee acknowledged long ago that Trump campaign adviser George Papadopoulos set off the investigation by bragging about Russia offering him "dirt" on Hillary Clinton.

This was reported to the FBI by the Australian government after hacked Democratic National Committee emails began to appear online months later. Based on his own acknowledgement in public reporting, we know that Carter Page, who had long been on the FBI's radar due to recruiting efforts by the Russian intelligence agencies, joined the Trump campaign, which then approved his trip to Moscow in July 2016. These are the facts that have been publicly reported. As with any investigation, there are many more facts that we will not know until the work is done.

Much has been made of the messages between FBI officials Peter Strzok and Lisa Page as a reason to terminate the investigation. Their texts criticizing candidate Trump were inappropriate, but after a yearlong investigation, the Justice Department inspector general "did not find documentary or testimonial evidence that these political views directly affected the specific investigative decisions that we reviewed." Indeed, the inspector general found evidence that in some instances Strzok and Page advocated for more aggressive investigative measures against Clinton. Courts have long held that motives of law enforcement are irrelevant in deciding whether a charging decision was lawful as long as there is probable cause to believe that a crime has been committed.

All this is to say that the Mueller investigation, legally and factually, is not "fruit of the poisonous tree." Do not just take our word for it, as the five guilty pleas speak for themselves. The defense attorneys representing these individuals, under oath in open court, disagree that critical evidence used to open the investigation was obtained illegally. Despite having access to nonpublic information, these five defendants never claimed that the FBI's investigation was improperly predicated or the "fruit of the poisonous tree." Those are just the guilty pleas. The special counsel has already resulted in federal grand jury charges against 23 individuals or entities with ties to Russia and the Trump campaign.

Mueller's recent court filing demonstrates that Vladimir Putin is still meddling in our elections and underscores the high stakes for our country. The intelligence community remains confident the Russian government directed the hacking of emails from the Democratic National Committee and Clinton's campaign chairman, and that the disclosures of these alleged hacked emails on sites like WikiLeaks are consistent with Russian efforts. We must get to the bottom of what happened. Curbing Russian aggression must be a priority for the United States.

We all need to put patriotism ahead of party. We still believe in American values that must always endure. No one is above the law, and people should be held responsible for crimes. Those are the principles of our democracy that we swore to defend. This is not a time for partisan misdirection dressed up as legalese. Let the facts come out. Let the special counsel complete his investigation.

Joyce Vance served as the United States attorney for the North District of Alabama from 2009 to 2017. Barbara McQuade served as the United States attorney for the Eastern District of Michigan from 2010 to 2017. They now teach at the University of Alabama and University of Michigan law schools.