Well, this is interesting....

President Trump’s letter to Speaker Pelosi on the State of the Union pic.twitter.com/B4QN9hDJnv

— Sarah Sanders (@PressSec) January 23, 2019

 According to McClatchy, Trump can enter the floor of the House of Representatives.  But the camera might not be on, the lights might not even be on, and he can't address a Joint Session of Congress if there has not been a joint resolution to hold such a session.  And that resolution can't come to the floor of the House without the approval of the Speaker.

Donald Trump is about to find out that the Speaker of the House is a Constitutional office of a co-equal branch of government.

Let's start with the joint session:

A joint session isn’t an ad hoc event. Both the House and Senate must formally agree to the session by adopting a “concurrent resolution.”

These resolutions are typically noncontroversial, often simply advanced by voice vote or what’s called unanimous consent, meaning no one objects so the measure is agreed to.

Pelosi, as the speaker, can control whether this resolution comes up for a vote at all in the House — or, if it does, she can urge her members to vote “no.” If there’s no joint session of Congress, Trump can’t come to the House floor to deliver his address.

Will anybody even be there?

Whether Trump could just get up on the dais and start delivering his State of the Union address is another question. Nothing could physically stop Trump from speaking in the House chamber, but there is a strict set of rules governing what is allowed to take place on the floor and what would be subject to condemnation.

In order for someone to deliver formal remarks in the House of Representatives, the chamber must be “in session,” which is at the discretion of the speaker.

And if the House isn't in session, and Trump walks into an empty chamber?

Ordinarily, C-SPAN is the only entity allowed to record House floor proceedings. But C-SPAN only has permission to operate when the House is officially in session. If the House isn’t in session and Trump comes to the floor and begins speaking, there would be no way of broadcasting the address to a national audience. The chamber lights might not even be on for Trump to see his written speech.

Can Trump demand other networks have access to the cameras?  No.  Can Trump demand the lights be turned on?  No.  Will this be a "Constitutional crisis"?  No; that would occur only if Trump got his way per that letter he sent to Pelosi.

Pass the popcorn.*

(In my mind's cinema I see the humiliation and rage as Trump's motorcade arrives at the Capitol and he enters the empty chamber, lights off, cameras dead.  Of course, to see that would require the lights be on and the cameras active, so I don't get my dream; but the effect will be like the tree falling in the forest that no one hears.  Trump may rage on Twitter, complain on FoxNews, but without the visual of his humiliation, who will really care (there is no Constitutional requirement that he make the speech to Congress, just that he deliver a report)?  And would he want to broadcast his powerlessness?  This is almost too perfect a victory over hubris and stupidity.)

ADDING:

“The fact is that we can understand, politically, the Speaker wanting to deny him the platform,” said [Andrea] Mitchell. “He wants the stage because he knows he can dominate.”

“He now wants that speech in that House as much as he wants to win the showdown,” replied [Margaret] Carlson, describing the standoff as “a preliminary bout.”

“He has to win it, because Trump has to be seen as a winner in his own mind or it’s debilitating for him,” she said, adding that she expected the president to win despite the shutdown. “That letter was spell-checked with all those exclamation points because he’s dead serious.”

Emphasis, obviously, added.  This is the best part of this nonsense; Trump cannot buffalo the Speaker of the House.  January 29 is much too far away. This is going to be like waiting for Christmas, all over again.