Ace in the hole" A hidden advantage or resource kept in reserve until needed, as in, "The prosecutor had an ace in the hole: an eyewitness." The term comes from stud poker, where each player is dealt one card face down—the so-called hold card—and the rest face up.

“To sit home, read one’s favorite paper, and scoff at the misdeeds of the men who do things is easy, but it is markedly ineffective. It is what evil men count upon the good men’s doing.”
– Teddy Roosevelt

And what action can be taken by House Dems to follow the Senate's action regarding Mexico and Canada tariffs? How to get Johnson's inaction out of the roadblock?

Not a filibuster; just good trouble