"You don't want your system of votes to be compromised in any way", Trump said during a joint press conference with Swedish Prime Minister Stefan Löfven.
"They can do whatever they like, but if they do that, then we put a big tax of 25 percent on their cars, and believe me, they won't be doing it very long", Trump said. "Whatever they do, we'll counteract it very strongly", the president said.
Trump's decision to impose tariffs on imported steel and aluminum have been met with heavy criticism from all sides of the political spectrum.
But Trump did hint that he was open to negotiating if the European Union removed some of its "horrible barriers", though he didn't mention specifics. "They make it nearly impossible for us to do business with them".
"I think its important for us to try to find a way to cooperate between the European Union and the USA", said Lofven.
Mr. Löfven came to the White House meeting with a stern warning that the European Union will retaliate if the USA goes ahead with planned tariffs on steel and aluminum.
Kelly on leaving DHS: 'God punished me, I guess'
Trump moved Kelly from DHS to the White House back in July 2017 to replace exiting chief of staff Reince Priebus. He said Porter had "presented himself as the ultimate gentleman" while he worked at the White House.
Russia special counsel Robert Mueller last month indicted 13 Russians and three organizations for meddling in the presidential election - and Moscow claimed Monday to have evidence the US has attempted to interfere in its forthcoming presidential vote. Trump was responding to a question from a Swedish journalist about what her country could learn from the American experience in 2016.
On Monday, Trump hosted Israeli Prime Minister Benjamin Netanyahu at the White House, and much of their discussion focused on the president's upcoming tariffs.
"I think they're honest also because the sanctions and what we're doing with respect to North Korea, including the great help that we've been given from China. Many, many people want every single job", Trump said when asked about the future of the embattled Sessions, whom Trump periodically tweaks on Twitter. "We haven't been given credit for this but we've actually been working very hard on the '18 election and the '20 election coming up".
"'Everybody wants to be there, and they love this White House, ' @POTUS says, disputing known challenges administration has in recruiting new personnel for West Wing as exodus publicly chronicled", The Hill's Alexis Simendinger tweeted.
It's not quite clear exactly what Trump is referring to in his remarks. But White House staffers have privately complained about difficulties attracting qualified candidates to the administration. "Probably there was meddling from other countries", he said. "And we can't lose our aluminum industry, also a fraction of what it once was".
Earlier in the day, North Korea and South Korea announced an apparent breakthrough in talks. "I was one of the first ones to say it".