Mets most recent trade with the Nationals was on March 30, 2015, when they acquired Jerry Blevins
The Mets and Washington Nationals have the longest trade drought of the teams listed here. On February 12, 2018, the Nationals did purchase Matt Reynolds from New York. This isn’t an actual trade so it won’t count.
We need to go back to March 30, 2015, to find an actual deal. On this day, beloved lefty reliever Jerry Blevins was dealt to the Mets in exchange for outfielder Matt den Dekker.
This seemingly unimportant trade with the Nationals turned out to be a pretty big one. Blevins is now a Mets-lifer, currently one of the major voices in the media for the team. He only pitched 5 innings for them in 2015 but had a major role in Terry Collins’ bullpen in 2016 and 2017. Blevins played four total seasons for the Mets and managed to go 14-4 with a 3.38 ERA while working primarily as a left-handed specialist.
In Washington, den Dekker had a decent year in 2015 as a part-time player batting .253/.315/.485 in 110 plate appearances. However, that would be his last season of significance. He managed to find his way back to the Mets in 2018 when he went hitless in 21 plate appearances.
The Nationals have been pretty good in the years since. Now in rebuild mode, maybe these two teams strike up a deal.