During the trip, Trump said Puerto Rico had pushed the federal government's budget "out of whack" and that the Maria death toll of 16 was low compared to the "real catastrophe" of Hurricane Katrina in New Orleans.
The president and his wife will travel to a local hospital to visit with patients and medical professionals, according to the White House schedule.
He praised police officers who responded to the scene, including those who were off-duty at the concert as well as "civilian heroes".
Sanders was speaking a day after Trump visited victims of a mass shooting in Las Vegas killed 58 and injured more than 500.
The store manager who sold a rifle to Las Vegas shooter Stephen Paddock said he feels "physically ill" knowing he interacted with the man who would go on to commit the deadliest mass shooting in US history.
Authorities have identified 64-year-old Stephen Paddock as the man who fired shots for between nine and 11 minutes from his 32nd-floor room at the Mandalay Bay Resort and Casino. "They're learning a lot more and that will be announced at the appropriate time".
"Our unity can not be shattered by evil, our bonds can not be broken by violence, and though we feel such great anger at the senseless murder of our fellow citizens, it is our love that defines us today - and always will, forever", President said.
"I think we all need to take a step back", she said during the daily White House press briefing. On Tuesday he called Paddock sick and demented. "There is no reason for them to buy something that makes the gun nearly fully automatic", said Mr Cohen.
Asked about gun laws, the president said "we'll be talking about gun laws as time goes by".
"Melania and I are praying for every American who has been hurt, wounded or lost the ones they loved so dearly in this bad, awful attack", he said.