The various goals were scrawled on a white board. Protest assignments were divvied up, like sign making and news media outreach. There was no consensus as to how to proceed, given the diverse interests motivating the protesters.  “I think disrupting, shutting down his speech, actually helps him,” said Greg Gelembiuk, 54, telling his fellow demonstrators that Mr. Trump has used clashes with protesters to portray himself as the aggrieved party and rally his base.  But there was more at stake than “trying to get Trump to shut up,” countered Stephanie Roades, 38, a longtime racial justice activist. The goal, she said, was to provide a counterbalance to all the hate and violence that has been on display at some Trump rallies. “He has legitimized a large group of people to act this way.”  Mr. Trump’s campaign declined to discuss its security precautions. It was clear, though, that the Trump sentries caught some but not all the protesters who passed before them, and that they also ensnared a reporter, who had no plans to disrupt anything, in their dragnet.  Ms. Roades was with 10 anti-Trump protesters who had planned to sneak in with signs that said things like, “No hate in our state” and “Hate is not a Wisconsin value.” But four of them were stopped at the door, Ms. Roades said, including herself.  Another one of those who were thwarted, Nathan Royko Maurer, 43, said he briefly made it inside but was ousted after taking a seat. Security approached him, he recalled, and said that he had been identified as a protester. “You’re going to have to leave,” they had said.  As it turned out, there was more action outside the site than inside. The Janesville police were looking for a man, who appeared to be wearing a red “Make America Great Again” baseball hat, who pepper-sprayed a 15-year-old protester who swung at a Trump supporter after, she said, she was groped.  There is a local flair to the Trump protest movement, with demonstrations largely carried out by activists on the ground at his various stops. But there is also some national coordination involving activist groups like Black Lives Matter, the Grassroots Global Justice Alliance, Mijente and Showing Up for Racial Justice, or SURJ.  Just this month, a group of activists formed the Stop Trump National Network to marshal those nationwide eager to block Mr. Trump’s White House bid.  Planning for the actions here started a couple of weeks ago, before Mr. Trump’s Janesville rally had even been announced. Members of Groundwork, an affiliate of Showing Up for Racial Justice, which encourages whites to fight against racism, held a conference call with national activists to discuss strategy.  In the local strategy sessions, people laid bare their preferences and anxieties. Ricky Diaz, a 28-year-old community organizer from Milwaukee, was pushing something visually dramatic, but not too noisy. He suggested someone dressing in a suit to represent Mr. Trump surrounded by people dressed as slaves. Kristen Brock-Petroshius, an organizer with SURJ, spoke of waking up at 4 a.m. one morning days before the rally in a fit of fear, stressing over what arrangements to make for her wife and children should she die in a protest.  Z Haukeness, a regional SURJ organizer, said they were not trying to stop free speech; rather, they were cracking down on what activists called hate speech.  A turning point in the effort to go after Mr. Trump in a more coordinated way came after a Trump supporter punched a protester as he was leaving a rally in Fayetteville, N.C., which garnered headlines. No one was talking about the 39 disruptions that protesters made during Mr. Trump’s speech, said Andrew Willis Garcés, who works with Showing Up for Racial Justice.  “At that point is when a lot of our folks are starting to feel like these one-off disruptions are not having the impact we want them to have,” Mr. Willis Garcés said.  Eventually, Wisconsin organizers developed a two-pronged approach. First, they tried to pressure the Holiday Inn Express to cancel the rally. After that failed, they sought to disrupt the speech itself.  The night before Mr. Trump was scheduled to appear, six protesters fastened themselves together with pipes wrapped in chicken wire and tape and sat down in the hotel lobby, demanding that the event be canceled.  After about four hours, the police cut the six protesters out of the restraints and arrested them.  While the Monday night sit-in received a lot of news media attention, Ms. Roades said the arrests left them a little short-handed for the Tuesday protest at the Trump rally. And so that left the much smaller group of 10, which was whittled to six by the time security screened the others. Of that group, only one person ended up protesting: Mr. Gelembiuk.  About 15 minutes into Mr. Trump’s speech, Mr. Gelembiuk slipped out two small banners from his jeans, turned his back to Mr. Trump and quietly held them over his head. One had a quotation from a prosecutor deriding Trump University. The other had a picture of Mr. Trump in clown face with the quote “White Flour!” as a play on white power.  After about 20 seconds, a few Trump supporters started shouting, “Trump! Trump! Trump!” — the signal that a protester was among them. Security quickly ushered out Mr. Gelembiuk from his back-row seat.  A version of this article appears in print on March 31, 2016, on Page A18 of the New York edition with the headline: Before a Trump Rally, Protesters Lay Plans Behind the Scenes. Order Reprints| Today's Paper|Subscribe
So conflict-prone have Donald Trump’s campaign rallies become that they have prompted an elaborate game of cat-and-mouse that takes place out of view of the television cameras.