The president fired State Department Inspector General Steve Linick, prompting Republican Utah Senator Mitt Romney to describe the move as a "threat to accountable democracy."
Mayor Giuseppe Sala of Milan said he would ask the U.S. consul to formally apologize for a World War II bombing in his city that killed almost 200 schoolchildren.
"The U.S. has no credibility to hold the moral high ground," a Global Times editorial claimed in response to a statement by Secretary of State Mike Pompeo.
A Global Times editorial suggested the official secrecy around the brutal suppression of pro-democracy protesters in 1989 has allowed the country to advance.
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.
The education secretary also reaffirmed her stance that states and local school districts should determine "the unique security needs in their local schools."
"Are we really prepared to say that we're powerless in the face of such carnage, that the politics are too hard?" Obama said after Sandy Hook. Trump agreed.