The Congressional Research Service has published a report; Russia's Nord Stream 2 Pipeline: Continued Uncertainty which summarises the overt actions taken by the US against the project.
Congress and successive U.S. Administrations have opposed Nord Stream
2 since the pipeline’s inception. Increasingly, congressional efforts
to block the pipeline have focused on sanctions, including through
progressively more stringent sanctions legislation enacted in 2017,
2019, and 2020.
In chronological order:
The Countering Russian Influence in Europe and Eurasia Act of 2017 (CRIEEA, P.L. 115-44, Title II) was incorporated into H.R. 3664: Countering America’s Adversaries Through Sanctions Act and signed by President Trump on August 2, 2017. It states that it is US policy to oppose the construction of the pipeline, and authorises sanctions on those who "invest at least $1 million, or $5 million over 12 months, or provide goods, services, or support valued at the same amount for the construction of Russian energy export pipelines".
In December 2018, the House of Representatives passed H.R. 1035 - a resolution expressing opposition to the construction of the pipeline, and supporting the imposition of sanctions.
The Protecting Europe’s Energy Security Act (PEESA) of 2019, which was incorporated into the National Defense Authorization Act for Fiscal Year 2020, and signed into law in December 2019 authorises the President to impose sanctions on foreign persons whom the President determines have sold, leased, provided, or facilitated the provision of vessels for the purpose of aiding the construction of Nord Stream 2.
At the end of 2020, PEESA was amended to extend sanctions to those "who provide underwriting services or insurance, or who provide certain upgrades or installation services" - although at the time of writing no sanctions authorised by PEESA have ever been imposed.
In January 2021, President Trump imposed sanctions under CRIEEA on Fortuna, the vessel being used to construct the pipeline, and its owner, KVT-RUS.