Robert Mueller's investigation into Russian interference in the 2016 election is coming under growing attack from those most blinded by partisanship and — in the case of the White House — self-interest. Their motivations do not automatically render them wrong. A dispassionate review of the facts, however, does.

Their assaults fall into three main categories. The first two are easily rebuffed. The third lands a punch — but not the knockout blow they seek.

• Discrediting Mueller. When President George W. Bush nominated Mueller, a fellow Republican, to lead the FBI in 2001, the Senate confirmed him by a unanimous vote. After he served his 10-year term, President Barack Obama gave him a two-year extension — and Senate support was again unanimous. Few people in Washington serving at the highest level of government can equal Mueller's reputation for integrity and independence.

Yet critics charge that Mueller is somehow compromised by his longstanding relationship with James Comey, his former deputy and successor at the FBI, who initiated the Russia investigation. Republicans have had a hate-love-hate relationship with Comey over the past two years, which says more about them than it does about him. Whatever one may think of how he handled his job, there is no evidence suggesting that Mueller is being influenced by him — or anyone else — in any way.

• Discrediting Mueller's work. Critics also charge that Mueller's team is on a fishing expedition that has found no evidence the Trump campaign colluded with Russia to influence the election -and thus should be shut down. They often cite the indictment of Trump's former campaign chairman, Paul Manafort, whose charges concern not his campaign activities but his work for a pro-Russian government in Ukraine.

But — leaving aside the seriousness of those charges — Mueller's mandate is to investigate not only Russian interference in the campaign, including any collusion, but also "any matters that arose or may arise" from the investigation. Manafort's actions certainly qualify, as do the lies of two campaign officials (both of whom have already pleaded guilty) about their contacts with Russia.

It's reasonable to expect Mueller to conclude the investigation in a timely fashion. But Congress cannot permit the White House to short-circuit his work.

• Discrediting Mueller's investigators. Mueller has assembled a team of top-notch investigators and lawyers with extensive experience on complicated, high-profile cases. Unfortunately, what's known about the team's political ties seems mostly to run in one direction.

Some have made campaign contributions over the years, with a few giving to Hillary Clinton. One of them, a cybersecurity and white-collar crime expert, represented Clinton in a case involving her private e-mails. Another represented a Clinton aide who helped set up the infamous private e-mail server. Then there are the private communications, such the anti-Trump text messages two investigators sent during the 2016 election, that have come to light and proved embarrassing.

Critics have seized on all this to conclude that the fix is in.

That goes too far. Lawyers of course have political opinions, but they routinely leave partisan attachments aside when prosecuting cases. One member of the team, for instance, donated to Obama and also won a conviction in a corruption case against a leading Democratic politician in New York.

Still, while federal regulations prohibited Mueller from inquiring about party affiliation, he erred in not sufficiently considering their political activities — knowing, as he surely must have, that public confidence in his team's objectivity and nonpartisanship would be critical to its credibility.

In such a high-stakes environment, it would be nearly impossible for any investigative team to avoid accusations of bias — though the unprecedented broadsides by Trump against the FBI will hurt its ability to retain and attract top-quality people, at no small cost to the administration of justice.

Where Mueller's investigation will lead is anyone's guess. But he and his team must be allowed to complete their work without being swallowed by the partisan plague infecting the land.