What are the facts on the border?

During his State of the Union address last week, Mr. Trump falsely cited El Paso as an example of a city where building a wall worked to deter crime.

“The border city of El Paso, Tex., used to have extremely high rates of violent crime — one of the highest in the entire country, and was considered one of our nation’s most dangerous cities. Now, immediately upon its building, with a powerful barrier in place, El Paso is one of the safest cities in our country,” he said.

[Read about what President Trump plans to discuss at his El Paso rally.]

But before the border barriers were completed in El Paso, in 2008, the city had the second-lowest violent crime rate among more than 20 similarly sized American cities. In 2010, after the fence construction, it retained its ranking. Also, El Paso was never one of the most dangerous cities in the United States.

How directly will Trump go after O’Rourke?

Mr. Trump relishes political combat and this is the first time in the 2020 election cycle that he will be on a dueling, if separate, stage with a Democrat who may try to unseat him. Mr. O’Rourke told Oprah Winfrey that he would make a decision about running for president by the end of February.

It seems a near certainty that Mr. Trump will try to counter the protest in El Paso and its unofficial leader, Mr. O’Rourke. How frontally he criticizes the former congressman, and whether he tries to brand him with a derogatory nickname will be measures of how seriously he takes Mr. O’Rourke’s potential candidacy.

What tone will O’Rourke use, fighter or healer?

Mr. O’Rourke is the near opposite of the president in tone. During his losing senate campaign last year, he offered himself as a candidate who could bridge divides and wanted to go beyond convenient party labels. That modulated approach is seen as part of his larger appeal. He was able to attract donations nationwide and build a following even as he lost his race.

Now he will face a different test in an opponent whose first instinct is to fight.

How will television cover the event?

Cable news outlets are expected to cover the rallies, and the president almost always takes priority over the words of someone who does not even hold elective office. This time may be different. At a minimum, prepare for a split-screen approach that will offer the freshest soundings of what promises to be a long and bitter presidential campaign.