WASHINGTON – As its trail of arrests gets closer to U.S. President Donald Trump, the Russia investigation is facing a multi-front assault. The attacks have ramped up following news that Trump’s close confidant Michael Flynn has pleaded guilty and become an informant.The president’s defenders are now seeking to poke holes in, and undermine, the investigation of special counsel Robert Mueller. Here are six avenues of attack:1.Mueller is biased: “It’s so disturbing and troubling,” Trump aide Kellyanne Conway told Fox News on Monday. She was speaking about weekend news that the Mueller probe removed a top investigator over the summer, after the discovery of texts to a lover blasting the president. This is atop reports that the same FBI investigator, Peter Strzok, was a key figure in the emails investigation that yielded no charges against Hillary Clinton. And there’s more: a paper trail of political donations shows several senior probe employees have a history of donating to Democrats. Another report said Strzok was involved in interviewing Flynn. Said Republican lawmaker Ron DeSantis: “It was almost as if they bent over backwards not to make the case on Hillary. With the Mueller probe, they’re just scorching the earth finding whatever little ticky-tack charge they can find on anyone… (Strzok’s role) undercuts the legitimacy of both those investigations.”2.Presidents can’t be charged for obstructing justice: This is potentially a key question. There’s evidence Trump tried thwarting an investigation into Flynn. The argument here is he’s allowed to. Trump lawyer John Dowd expressed it via the Axios website: “The president cannot obstruct justice.” Harvard scholar Alan Dershowitz says Trump has constitutional power — to pardon Flynn himself, to fire the FBI director, and to issue instructions to the Justice Department. So what’s the legal problem if he orders the FBI to lay off Flynn, Dershowitz asks: “We’d have a constitutional crisis (if Trump is charged with obstruction),” he told Fox News. “You cannot charge a president with obstruction of justice for exercising his constitutional power.” He says presidents can only be charged with obstruction that involves innately illegal acts — like the Nixon White House destroying evidence and paying hush money. Other legal scholars call this a laughable, quasi-regal, anti-democratic argument. One headline on the Vox website said, “Trump’s lawyer: the president can’t obstruct justice. 13 legal experts (say): yes, he can.” A list of law professors cited legal precedents, and the fact that the president’s power comes from the Constitution — the same Constitution that says he must faithfully execute the law. Peter Shane of Ohio State University called the Dershowitz-Dowd argument “nonsense.”3. It’s a nothing-burger: They say this investigation is built on a flawed foundation. Mueller’s probe was struck to examine collusion with Russia — during the election. His critics note that four people are now charged — two for financial crimes predating the election, two for lying to the FBI after the election. This view is articulated in a Washington Examiner piece, “Was it all about the Logan Act?” In this narrative, the root of the probe is a dust-gathering, never-used law from 1799, the Logan Act, which forbids people from undermining U.S. foreign policy: Flynn spoke with Russians during the presidential transition; the FBI then questioned him about it; Flynn lied; he and James Comey were forced out; Flynn was charged; now he’s a co-operating witness against Trump. A closely related argument involves the notorious Steele dossier — a document filled with jaw-dropping allegations that the Russians spent years recruiting Trump as an asset, and collecting blackmail material on him. The document was gathered by a former British spy and handed to the FBI. But his original customers were Trump campaign opponents. Critics now argue that any evidence stemming from this dossier is illegitimate. Others say this entire line of attack is wishful thinking — there are already several documented communications during the campaign with Russians, or suspected Russian intermediaries like Wikileaks, and some other investigation targets, like Paul Manafort, had reportedly been under surveillance for years.4. Cut off funding: This is reportedly the route suggested by Steve Bannon. Trump’s ex-staffer, and still-ally, doesn’t want him to fire Mueller. He’s publicly said so. What he’s urging, reports say, is that Congress slash Mueller’s funding. That view is articulated by pro-Trump congressman Steve King, who told Politico: “For them to say to us, ‘Vote for an open-ended appropriation into a Mueller witch hunt,’ I think you’ll see significant objection.”5. Fire Mueller: Several Republican lawmakers have introduced a motion calling for Mueller’s recusal over alleged conflicts of interest. The Wall Street Journal editorial page urged him to resign, given his personal friendship with a key witness, Comey. Some conservative groups like Judicial Watch are calling for Mueller to be fired. A Canadian friend of Trump’s doesn’t go that far. Conrad Black says Mueller should simply be reined in. Black calls the investigation a “never-ending fishing expedition” and suggests a series of moves aimed at keeping it in check — replace the secretary of state with the director of the CIA; appoint to the CIA Attorney General Jeff Sessions, who has recused himself from Russia-related matters; have Dershowitz replace Sessions; and get Dershowitz to limit the probe to its main purpose: Russian involvement in the 2016 election.6. Rally the base: Ultimately, politics could decide all of this. Trump’s fate could eventually rest with Congress, given the legal realities — the president’s power to pardon; doubts about whether a sitting president can be charged; and the aforementioned debate about obstruction of justice. Impeachment, the ultimate political punishment, requires a two-thirds vote in both chambers of Congress. That’s 290 in the House, 67 in the Senate. It means more than 100 Republicans would have to turn on their president. And the full-throated assault on Mueller — from Trump’s Twitter feed, Fox News, and conservative news outlets — provides a daily rallying cry for the ranks to remain united.Note to readers: This is a corrected story. An earlier version said Steve King was a senator, and that Conrad Black suggested bringing in a new attorney general to fire Mueller.