American President Donald Trump on Monday condemned the weekend mass shootings in Texas and Ohio that killed 31 people and injured many others.On Saturday, a gunman killed 22 people and wounded 24 others at a Walmart store in El Paso, Texas.Many were shopping for back-to-school clothes and supplies for their children.The suspected shooter has been linked to an online document denouncing immigrants, especially the Hispanic population in Texas.The U.S. Justice Department is "seriously considering" bringing federal hate crime charges against the suspect.About 13 hours later, another gunman shot at a crowd in a busy nightlife area in Dayton, Ohio.Nine people were killed and 16 were wounded.Police killed the gunman within 30 seconds of his first shot.City leaders say such fast action by police may have saved hundreds of lives.Trump addressed the nation on Monday.Speaking from the White House, he said, "In one voice, our nation must condemn racism, bigotry and white supremacy."The president then blamed social media, the internet, video games, and mental health for mass killings in America.Trump called for "red flag laws" that would permit the removal of firearms from people with mental health problems.He said, "Mental illness and hatred pull the trigger. Not the gun."The president also talked about expanding background checks for gun users.Trump did not provide details or take questions from reporters.Earlier in the day, Trump suggested on Twitter that Congress could tie "strong background checks" with "immigration reform"for new legislation to address the violence that took place in El Paso and Dayton.Trump did not explain how the two issues are connected.The suspects in both shootings were white, male U.S. citizens.Former U.S. Vice President Joe Biden is a leading candidate for the Democratic nomination to run against Trump in the 2020 presidential election.He answered Trump's tweet. He wrote, "Mr. President, immigration isn't the problem. White nationalism is the problem."Biden added, "It's time to put politics aside and pass universal background checks and an assault weapons ban."Another Democratic candidate, Senator Cory Booker of New Jersey, noted,"White supremacy is not a mental illness, and guns are a tool that white supremacists use to fulfill their hate."After the 2018 school shooting in Parkland, Florida, Trump promised to be "very strong on background checks."He also said he would stand up to the National Rifle Association, a pro-gun group, in order to stop the violence.But earlier this year, Trump threatened to veto two gun-related bills passed by the Democratic-controlled House of Representatives.Trump said the bills would not provide enough protection for gunowners' rights.One bill would require federal background checks for all gun sales and transfers, including those sold online and at gun shows.The other would give investigators more time to do background checks.The Republican-controlled Senate has so far refused to consider the House bills.Fifty-seven percent of Americans support stronger gun control laws, according to a 2018 study by the Pew Research Center.