Rescue efforts at the site of a partially collapsed Florida condominium building resumed Thursday evening after a 15-hour pause for safety concerns, and officials said they had started planning for the likely demolition of the remaining structure.Miami-Dade County Mayor Daniella Levine Cava said the decision about the demolition needs to be made "extremely carefully and methodically," considering the potential impact on the pile of debris and the effect on the search-and-rescue operations. An engineer from the Federal Emergency Management Agency said it would likely be weeks before officials schedule the demolition.The rescue work was halted shortly after 2 a.m. amid concerns about the stability of the part of the tower that still stands. Crews noticed widening cracks and up to a foot of movement in a large column.Work resumed shortly before 5 p.m. after the site was evaluated by structural engineers, Cava said, describing firefighters as "really, really excited out there.""We will continue to search feverishly, as we have done all along in the parts of the collapse that we currently have access to," she said.Scott Nacheman, a FEMA structures specialist, said operations were paused after sensors detected movement. It was later determined that the building itself had not moved, but there was movement in the debris pile below and in debris on the building "of significant size," Nacheman said Thursday.Nacheman said additional sensors were added to the site."Right now, we're in a position where we feel it is safe to continue operations. We've done so, and monitoring will continue indefinitely until the operations are complete," he said.The stoppage had threatened to dim hopes for finding anyone alive in the debris a week after the tower came down. Surfside Mayor Charles Burkett said the halt was worrisome since "minutes and hours matter, lives are at stake."The rescue operations unfolded on the same day that President Joe Biden and first lady Jill Biden visited the devastated community.The collapse of the 12-story Champlain Towers South beachfront condominium killed at least 18 people and left 145 missing. No one has been rescued since the first hours after the collapse."This is life and death," Biden said during a briefing. "We can do it, just the simple act of everyone doing what needs to be done, makes a difference.""There's gonna be a lot of pain and anxiety and suffering and even the need for psychological help in the days and months that follow," he said. "And so, we're not going anywhere."Crews noticed several expansions in cracks they had been monitoring. They also observed 6 to 12 inches of movement in a large column hanging from the structure "that could fall and cause damage to support columns" in the underground parking garage, Miami-Dade Fire Rescue Chief Alan Cominsky said.Heavy equipment in the rubble pile caused vibrations, according to Nacheman. Rain has also been entering exposed parts of the building, saturating items and adding weight to the floors.Peter Milián is a cousin of Marcus Guara, who died along with his wife, Anaely Rodriguez, and their two children, 10-year-old Lucia Guara and 4-year-old Emma Guara. Milián said he understood why the rescue work had to be temporarily halted."I mean, they've done everything they can. But we trust the people that are on the ground. And obviously, they've got to do what's best for their people, right? Because it is a dangerous situation," he said.During a private meeting with family members, Biden drew on his own experiences with grief to try to comfort them. Biden lost his first wife and baby daughter in a car crash and decades later lost an adult son to brain cancer."I just wish there was something I could do to ease the pain," he said in a video posted on Instagram by Jacqueline Patoka, a woman who was close to a couple and their daughter who are still missing.Biden spoke of wanting to switch places with a lost or missing loved one. "The waiting, the waiting is unbearable," he said."The people you may have lost — they’re gonna be with you your whole life," he told the families. "A part of your soul, a part of who you are."Biden told the families that it can be "harder to grieve in public than it is in private, so I know there's an extra burden on you all.""But I promise you: I still believe in prayer," he said. "You're in my prayers."The cause of the collapse is under investigation. A 2018 engineering report found that the building's ground-floor pool deck was resting on a concrete slab that had "major structural damage" and needed extensive repairs. The report also found "abundant cracking" of concrete columns, beams and walls in the parking garage.Just two months before the building came down, the president of its board wrote a letter to residents saying that structural problems identified in the 2018 inspection had "gotten significantly worse" and that major repairs would cost at least $15.5 million. With bids for the work still pending, the building suddenly collapsed last Thursday.