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WASHINGTON — The Russia probe is no longer just an abstraction or a distraction for President Donald Trump. It’s now a legitimate full-blown Washington scandal — the kind that can subsume a president’s agenda or destroy his party at the polls.

The immediate question is whether Trump, a master of messaging, can keep himself and his allies focused on policy goals while the investigation into whether his campaign colluded with Russia intensifies.

That’s been a tough task — though not always an impossible one — for past presidents. Richard Nixon was ultimately undone by Watergate, but Ronald Reagan survived the Iran/Contra affair and Bill Clinton managed to strike landmark legislative deals during the Whitewater scandal.

"You can’t just ignore it, but at the same time, you can't allow it to become the driving force," said Tom Griscom, who was brought in as Reagan's White House communications director during the Iran/Contra investigation. "It ought to be business as usual. … You’ve got an agenda, and that's where their focus ought to be."

The good news for Trump is that Republican lawmakers who control Congress will certainly want to stay focused on their policy agenda, particularly the tax reform package they’re hoping to enact later this year.

"Nothing’s going to derail what we’re doing in Congress," House Speaker Paul Ryan said Monday on WTAQ radio in Green Bay, Wisconsin.

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"I think this sort of news has been baked into most peoples' assumptions for some time now," said Michael Steel, a former House Republican leadership aide. "Congressional Republicans have become adept at ignoring 'noise' and focusing on their agenda."

The bad news: Trump has trouble staying focused on substance, even — or especially — when it's in his best interests to do so.

On Monday morning, he entered the fray by arguing that one of the indictments, against his former campaign manager, Paul Manafort, dealt with issues that pre-dated Manafort's work for Trump.

Sorry, but this is years ago, before Paul Manafort was part of the Trump campaign. But why aren't Crooked Hillary & the Dems the focus????? — Donald J. Trump (@realDonaldTrump) October 30, 2017

....Also, there is NO COLLUSION! — Donald J. Trump (@realDonaldTrump) October 30, 2017

But it wasn't just Manafort and longtime business partner Rick Gates who made headlines on Monday. Special counsel Robert Mueller secured indictments against them, but he won a secret guilty plea from George Papadopoulos, a campaign foreign policy aide who lied to the FBI about contacts he had with agents of Russia. One of his contacts, an "overseas professor," said in early 2016 that Moscow had "dirt" on Hillary Clinton, in the form of "thousands of emails," according to the plea agreement.

Clinton campaign chairman John Podesta's personal emails were published by Wikileaks on a rolling basis every day in the last month of the campaign.

The Papadopoulos conviction makes it impossible for Trump to play down the significance of Mueller's investigation, said Ron Klain, a former chief of staff to Vice Presidents Al Gore and Joe Biden who helped Clinton with debate prep sessions during the 2016 campaign.

"We now know that the Trump campaign was aware that Russia had hacked Clinton campaign emails before it was public, that a top adviser to Trump tried to conspire with Russian agents to get those emails, and that the Trump campaign chair owed huge, shady sums to Russian allies," Klain said.

"On the eve of Halloween, any ongoing effort by Trump to claim that the Mueller investigation is just a 'witch hunt' has been blown to pieces," he added.

It won't be clear for a year or so whether the Russia probe affects the fortunes of Republican candidates for the House and Senate, but former Rep. Tom Davis, R-Va., said "it's not helpful" to them.

"What it does for the Democrats is embolden them," he said. "For Republicans, it just depresses them."

The bigger issue, Davis added, is whether voters believe Republican lawmakers have delivered on their legislative promises come next November.

And that's why the GOP is hoping Trump can stay focused while the Mueller probe swirls around him.