Top Democrats poised for powerful roles next year are demanding that major banks and ports preserve any records they have tied to potential imports or other deals involving Russian diesel.

Why it matters: Probing President Trump's agreement with Moscow will be a priority if Democrats regain control of either or both chambers of Congress.

The new demand shows that inquiries will extend beyond the White House and into C-suites.

Driving the news: "[A]ny importation of Russian diesel into the U.S. raises significant legal questions and may be subject to legal action, as well as congressional investigations," a new letter obtained by Axios states.

It's signed by Sens. Chris Coons (D-Del.), Elizabeth Warren (D-Mass.), Ron Wyden (D-Ore.), and Sheldon Whitehouse (D-R.I.).

They're in line to lead the powerful Foreign Relations, Banking, Finance and Judiciary Committees, respectively, if Democrats regain the Senate.

Rep.…