"Well, we're looking at it. People have a right to do what they want to do. I think it's something that I've been looking at and I've been thinking about and I'm the one that brought up the pipeline problem," Trump told reporters during an appearance with Polish President Andrzej Duda.
Trump has claimed since last year that Germany is captive to Russian energy exports. Like past U.S. presidents, he opposes the Nord Stream 2 pipeline, which would run beneath the Baltic Sea alongside an existing line linking eastern Russia and northern Germany.
The U.S. and many European nations fear the pipeline would help Russia bypass infrastructure in Ukraine, allowing Moscow to use energy supplies as a weapon against its neighbors without disrupting flows to Western Europe.
Russia and Germany assert Nord Stream 2 is a purely economic project. Russian energy giant Gazprom is building the line, with financing from European companies including Royal Dutch Shell and Wintershall.
Sen. Ted Cruz, R-Texas, and Sen. Jeanne Shaheen, D-N.H., last month filed a bill that would impose sanctions on vessels used to build Nord Stream 2. Energy Secretary Rick Perry and other administration officials have also raised the prospect deploying sanctions to block construction.
The Trump administration is seeking to displace Russian pipeline supplies to Europe with U.S. exports of liquefied natural gas, a form of the fuel chilled to liquid form for transport by tanker ship.
On Wednesday, the Polish Oil and Gas Co. signed an agreement to purchase an additional 1.5 million tons per year from Venture Global's proposed Plaquemines LNG export terminal south of New Orleans. The deal increases the Polish state-controlled company's committed purchases from Plaquemines to 2.5 million tons per year.