The danger President Trump faces from the various investigations into the Trump-Russia matter has changed dramatically in recent weeks. If you're a Republican and you still believe the critical question is whether Trump or his associates colluded with Russians to influence the 2016 election -- if you still think that, you're behind the times. So now, a few notes on where the Trump affair is today:

1. It's not about collusion anymore

Fired FBI Director James Comey's testimony before the Senate Intelligence Committee marked the full shift of the Trump-Russia investigation from a probe dedicated to discovering collusion to a probe dedicated to proving the president obstructed justice. (See "At this rate, it won't matter if Trump colluded with Russia.") Democrats at the Comey hearing barely touched on collusion, which appears to have turned out to be a dry hole. When it did come up in Comey's appearance, it was during questioning from Republicans, who wanted to highlight their point that collusion -- the core of the case and the reason everybody got so excited in the first place -- has so far turned out to be nothing.

To Democrats, that no longer matters. Now, it's all about obstruction of justice, or alleged obstruction of justice, or fantasized obstruction of justice, depending on your partisan perspective. Senate Democrats focused almost exclusively on obstruction in their questioning of Comey, and their House counterparts are sure to do the same. As far as the Justice Department investigation of the president is concerned, we know that as of the time Comey was fired on May 9, there was no investigation of the president concerning collusion, which strongly suggests that after 10 months of probing, authorities had nothing against him on that issue. Now, however, after the Comey memos and the Comey firing, it seems safe to predict that special counsel Robert Mueller will investigate Trump for obstruction. So it is a new game, even if Republicans keep trying to play the old one.

2. Trump failed to take the threat against him seriously

Here is a simple fact: Many of Trump's most determined adversaries do not want just to defeat him on Obamacare, although they want that, too. They do not want just to defeat him on taxes, although they want that, too. They do not want just to stop the border wall, although they want that, too. No, they do not want just to defeat him -- they want to remove him from office.

That has been clear from the moment the Associated Press called the presidential race for Trump in the early hours of November 9. Some of those adversaries began discussing ways to remove Trump -- the 25th Amendment? Impeachment? -- that very day. Some Democrats have been talking about it ever since.

What seems clear, though, is that Trump never, at least until now, took the threat terribly seriously. Whether from his own belief that he can persuade people to like him, or his faith in his ability to do business with a wide variety of players -- for whatever reason, Trump has acted as if he is not every day in mortal threat from opponents who want to remove him from office. He has given them ammunition left and right and then complained that they are using it.

Will Trump change now, after all the damage that's already been done? Certainly he is receiving advice to do so. But so far his efforts to lawyer up and fight back, Washington-style, have been spotty.

3. The future is in Robert Mueller's hands

There are a few models for how the Mueller investigation might play out. The Kenneth Starr-Whitewater model from the Clinton years will not apply because there is no independent counsel statute -- the law that in essence created an Office of Permanent Investigation for the scandal-prone Clintons -- that can keep probes going for years and years. Perhaps more relevant, and equally ominous, for Trump is the Patrick Fitzgerald-Plamegate investigation of the George W. Bush years. There was an underlying crime in that matter -- the leak of CIA employee Valerie Plame's identity -- but Fitzgerald knew who did it even as he started the investigation. Fitzgerald never prosecuted that person or anybody else for an underlying crime and instead spent more than three years dragging Bush figures before a grand jury and finally prosecuting one, Lewis Libby, for perjury and obstruction.

Mueller could certainly follow that path if he chooses. But some on Team Trump believe -- hope? -- that he won't, given a career they believe shows good judgment and a straight-down-the-line-not-a-zealot-like-Fitzgerald style. Perhaps the most hopeful factor for Trump is this: Fitzgerald was 43 years old when he was appointed. Starr was 48. They had years to give to their pursuits. Mueller is 72. Team Trump is hoping he's not interested in chasing this investigation till he's pushing 80. (On the other hand, Iran-Contra independent counsel Lawrence Walsh pursued his investigation for seven years, until he was 81 years old.)

4. More evidence? Democrats don't need any more to impeach

How many times have you heard a Democrat or Trump critic say that the Russia investigation is "just getting started" or that they are determined to "get to the bottom" of it? With a new prosecutor starting an open-ended investigation, they're hoping for years of happy hunting. But the fact is, Democrats do not need any more information than what is already publicly known to pursue impeachment proceedings against the president. What they need is 218 votes in the House of Representatives. If they had majority control of the House now, they would already be pursuing impeachment. Which means…

5. 2018 is everything

In 2006, when the Iraq War was going disastrously and George W. Bush was weakened not only by the war but by his tin-eared reaction to Hurricane Katrina, a number of House Democrats saw not only victory coming in the November 2006 midterms but impeachment as well. Democratic Rep. John Conyers, who stood to become chairman of the House Judiciary Committee if his party won that year, was a big impeachment advocate who relied heavily on something called the Downing Street Memo, which was a British intelligence document that supposedly proved Bush lied about Iraqi weapons of mass destruction.

But even though Bush was politically weak, Nancy Pelosi, who stood to become Speaker if Democrats won, was wary of making the 2006 midterms a referendum on impeachment. Knowing that voters want to vote for something more positive than punishing a president -- for example, policies that might make their lives better -- Pelosi flatly declared before the election that if Democrats prevailed, impeachment would be "off the table." As it turned out, she won big, became Speaker, and impeachment stayed off the table.

Now, Democrats have a new class of impeachment enthusiasts who want to go after Trump as soon as possible. And Pelosi, who likely would again become Speaker if Democrats take the House in 2018, is again counseling caution.

In the end, though, it all depends on the facts of the Trump-Russia case. If there are piles of new and damning evidence that emerge between now and November 2018, that will certainly encourage some Democrats to run on impeachment. But if Trump-Russia is still a story in which a reasonable person could determine that the president did nothing to warrant removal, then Democrats face a danger in appearing over-eager to bring down Trump. One could even imagine Republicans using the issue against Democrats, charging that the only plan they have if elected in 2018 is to impeach the president, as opposed to, say, trying to improve the voters' lives.

Whatever the case, the bottom line next year is 218 votes. If Democrats have them, the president's life becomes much, much more difficult and fraught with danger.