"This is something that I have been looking at, and I am thinking about," Trump said when asked by reporters about possible US sanctions against the pipeline.
Trump, who was speaking during Polish President Andrzej Duda's visit to the White House, said he was the first person to propose doing something about what he called "the pipeline problem."
"I'm the one that brought up the pipeline problem where you have Russia giving a tremendous percentage of energy. You know this gas is going into Germany. I say, 'How can you do that?'" Trump said.
"Germany is making a tremendous mistake by relying so heavily on the pipeline, it’s a mistake for Germany. But again, Germany’s running their affairs, and they do just fine. I was critical. I’ve been critical of it. It’s a tremendous amount of their energy that will be supplied by that pipeline," Trump said.
Nord Stream 2 is a joint venture of Russian energy giant Gazprom and five European companies. It aims to deliver 55 billion cubic meters (1.9 trillion cubic feet) of Russian natural gas annually directly to Germany and other European countries through a twin pipeline laid at the bottom of the Baltic Sea.
Meanwhile, the United States, which seeks to promote its liquefied natural gas in Europe, has been one of the most vigorous opponents of the construction of the Nord Stream 2 pipeline and has called on Gazprom's European partners to withdraw from the project or potentially face sanctions.