Trump said his offer to the Mexican government to "let us go in and clean it out" was rejected.
A controlled border could stop most of the drugs coming north and most of the guns flowing south.
"The only thing that can counteract bullets is more and bigger bullets," GOP Senator Tom Cotton said.
Fox News host Brian Kilmeade joked Wednesday morning that the people of Mexico would just return to "work in the fields" if their president refused to declare another war on drug cartels.
The Florida senator says U.S. military action in Venezuela is "always" an option, citing the unstable presence of drug cartels, Marxist militant organizations and "hundreds" of Russian military advisers in the South American nation.
Vampire bats' venom contains a compound that could revolutionize the treatment of serious medical conditions, researchers say.
Mexico's Veracruz state government said the police had not been properly trained to handle firearms, but a city mayor says the decision is politically-motivated.
Fernando Ángeles Juárez was shot dead by gunmen on Thursday, prompting federal police to detain every officer in the Mexican town of Ocampo.
Fernando Puron was killed in the northern Mexican state of Coahuila.
Known as the "narcos of narcos," Caro Quintero was in prison in Mexico for 28 years before being released in 2013 over a technicality.
The Justice Department charged CEO Vincent Ramos and his associates of racketeering and conspiracy to facilitate drug distribution.
The group issued a warning to their rivals following the execution.
More than 1,900 homicides have been registered in Guerrero state this year.
Joaquin "El Chapo" Guzman, who escaped from two Mexican prisons and was a key figure in a bloody drug war, is seen as a flight risk by the U.S. government.
Building a wall is expensive symbolism; it won't prevent catapults, submarines or laundered cartel money.
Police corruption has been in focus since police officers were charged with kidnapping and murdering a Korean businessman.
President Rodrigo Duterte has told police they may "shoot to kill" drug dealers.
Those trying to stop the ivory trade can learn from people tackling drugs trafficking.
Women reported being arbitrarily arrested and sexually abused by police and the military.
Early on Saturday, Guzman was moved to a high security prison in the northern city of Ciudad Juarez on the U.S. border.
"They say they aren't punishing him, but they certainly are," the wife of 'El Chapo' says in her first-ever interview.