They have to know it’s DOA... why would they waste their time?
They are not wasting their time.
It is about the optics. Trump DOA’s their plan and Democrats can whine about it for months to come.
It is a political ploy and trap being done to set things up for elections in 2018
So they can scream “He won’t work with us! He lied — he said he wanted to build infrastructure! LIAR! LIAR!”
So they can say they're trying to reach out to him, but when he vetoes it, media-hogs Graham, McCain and Schumer can do what they love (which isn't representing the interests of their respective states) which is go in front of the media, and say that Trump doesn't care about the infrastructure of the country.
I really, really hope he understands the game they're playing. Not to insinuate he doesn't know the gamesmanship, but he has to say no at every juncture.