Contact Senators Sanders (VT), Merkley (OR), Gillibrand (NY), Hirono (HA) Markey (MA) and Warren (MA) and thank them for writing this letter in support of the peoples' trade agenda. You can also print a copy of the Senators' letter and mail it to your own US Senators, expressing your support for it and your desire that they sign a copy and mail it to the President as well.
Letter here.