Two excerpts, prompted by me wondering, re the caravan: why just now (it won't get to the Mexico-US border prior to the election, if "it", the caravan however defined, gets to that border at all)?: 

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The size of the caravan has led a lot of people to assume that someone must be organizing and supporting it. A video that appears to be from near the start of the caravan route, which shows money being handed out to women, has been used by conservatives in the US as evidence that the caravan is a liberal plot (Florida Republican Rep. Matt Gaetz has blamed George Soros) and by the Honduran government as evidence that Fuentes and Libre, the political movement to which he belongs, are behind the caravan.

But whatever that video actually captured, it doesn’t represent the truth of the caravan as it’s continued into Guatemala and Mexico — a straggling procession of people relying on humanitarian organizations and sympathetic locals for food, transportation, and medical assistance.

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5) Why is Trump obsessed with the caravan?

The short answer is b-roll.

B-roll is a TV industry term for the brief clips that run on mute to illustrate a segment while an anchor is narrating or a talking head is commentating. If a channel is giving a lot of coverage to a particular story, the b-roll clips it has for that story will get a lot of play — making it hard for any but the most dedicated viewer to tell when or where something happened, or even whether it’s happened more than once.

Caravans make for evocative b-roll: masses of people pressing toward the United States. Fox News leaped on the story of the caravan the minute it reached Guatemala with captions that talk about a press of people at the “border” and only a tiny note in the corner identifying that “border” as a Central American one.

And the president, Fox News-watcher-in-chief, has taken his cues on the caravan from the cable news channel. He started railing about it when Fox started covering it on October 16.

The caravan is a perfect obsession for Trump for the same reason it’s a perfect obsession for Fox: powerful images that appear to validate conservative base fears of “invasion” by “lawless” foreigners and the countries that “send” them. Trump himself has been using imagery like this since he started his presidential campaign in 2015 and talked about Mexico “sending” rapists and murderers over the US-Mexico border.

The caravan has provided more fodder. It’s a constant motif of his near-daily rallies and his morning and evening tweetstorms as the midterm elections approach.

His rage is being fed by hardliners in the administration who want to do more to crack down on families and asylum seekers at the US-Mexico border (options being considered include forcing parents to choose between months-long detention and family separation). It’s also being fed by Fox.

Other Republicans were already following Trump’s lead in making immigration their key issue in the closing weeks of the midterm campaign, amid concerns that the Republican base won’t turn out without Trump on the ballot. They’ve followed his lead on the caravan too. While GOP hardliners within the administration are using the caravan as a reason to push for a change to the laws governing children and asylum seekers who arrive at the border, Republicans have turned the caravan into a reason that Democrats shouldn’t be allowed to take Congress — because they would let in untold numbers of migrants.

The Trump administration absolutely believes this is the way to fire up the Republican base for the midterms. But it’s hard to tell how much of this is deliberate strategy and how much is Trump’s personal obsession — or if there’s any difference between the two.

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One possible explanation, an innocuous one, to the question of why now?, just before crucial US elections, is that efforts to cross the border into the US are ongoing, and that caravans, for reasons explained in the article, offer a reduced risk of abuse or worse from government authorities, for individuals traveling as part of them.

There are other, less innocuous, possible explanations.  As the beginning of the article hints at.  I don't put much of anything at all past Republican party and right wing extremist tricksters.  The optics of the caravan alone make the Republican task of distraction from issues and numerous other developments they don't want garnering attention easier. 

It's not lost on this observer that people like Gingrich have recently been pushing the caravan as a (he wishes) deciding factor in these election outcomes.  No one knows whether it will turn out that way or not.  It isn't difficult to imagine the current crop of Republicans seeing this as their best play right now, to just keep the image of the caravan flashing on TV screens 24/7 on Fox and wherever else they can.  They don't have much else besides fear-inducing images right now.