ANALYSIS: In Comey testimony, Trump faces showdown with forces he unleashed

The wild and unpredictable forces that have been unleashed by President Donald Trump will swirl together this week, when James Comey walks into the Hart Senate Office Building on Thursday.

It will mark a rare moment of focus in the midst of a presidency that has regularly courted chaos. Still, extraneous forces are bound to make themselves known -- just as Trump has failed to quiet his own urges to tweet even as his team tries to bring message discipline to the White House.

Comey, the fired FBI director, represents more than a political foe. He is a career law-enforcement professional who was removed from his job by the president as part of his effort to take on the intelligence and Justice Department establishments, all part of his broader attempt to remake Washington.

Comey's firing marked either a high point or a low point in Trump's effort to change Washington, depending on one's perspective. He's either a symbol of incompetence and insubordination, or a noble public servant who lost his job because he was willing to stand up to the president of the United States -- and might have been learning uncomfortable truths about his inner circle.

Either way, Comey's day in the spotlight figures to be a signal moment in the Trump presidency. Major storylines of the Trump era -- Russia ties and investigations into the Trump orbit, the chaotic and impulsive leadership style of the president, the attempts to remake the federal government -- will be intertwined.

In the middle of it all will be Comey. He has the potential to rock a presidency, depending on how he describes purported loyalty pledges and presidential efforts to intervene in an investigation.

And extraneous forces figure to be just as relevant to anything said this week. Just don't expect the messaging from the White House to bring with it any more discipline than the president himself displays.

The White House entered the week by announcing plans to refocus the agenda on infrastructure projects. But before sunrise Monday, Trump had picked a fight with the mayor of London, based on a casual misinterpretation of something the mayor said after a terrorist attack.

A debate has raged online and on cable television about whether the president's tweets represent official presidential statements. In the midst of that, the president has gone on the attack over his proposed travel ban, taking on the courts and even his own Justice Department in a series of statements that can't be of help in court proceedings.

In other words, it's just another week in the Trump presidency, and the main event is still days away. On the Comey front, White House officials and allies have previewed their responses by pointing out inconsistencies and inaccuracies in his previous testimony -- and by reminding people of how reviled he was by Democrats before Trump decided to fire him.

That sets the default mode where Trump prefers it: attack. Trump has been at his most comfortable when he's picking fights; his challenge now is facing off against an adversary who just might have the weapons to fight back.