As we head into the fall's legislative fights and the new year, we'll be watching President Trump's deep frustration with the Senate in general and Mitch McConnell in particular. Sources who've spent time with Trump privately say he's at his wits end with both.

"Mitch isn't up to it," Trump privately tells associates, arguing that McConnell is a failed leader, past his prime, without the strength or stamina required to ram through his agenda.

Trump gets a kick out of his favorite TV host, Lou Dobbs, who constantly trashes GOP congressional leaders. (The president often calls Dobbs to praise him on his shows, revel in his attacks on Paul Ryan and Mitch McConnell and to seek his opinions on various issues.)

Trump views the Senate as an extension of McConnell: an archaic, do-nothing institution that relies on old rules simply because they are traditions, and not because they serve any modern day purpose. Trump's constant tweeting about the need to abolish the legislative filibuster — so Republicans can ram through any bill with 50 rather than 60 votes — can also be read as jabs at McConnell, who has bluntly said he won't change this tradition. (Asked about this, a White House official said the president has made his frustrations with the filibuster clear and his comments have been directed at the entire GOP caucus rather than any one individual.)

What's next: It's an open question whether the breakdown of the Trump-McConnell relationship will make this year's goals harder to achieve — Congress must agree to fund the government by the middle of December, Republicans have pledged to pass their tax plan this year, and the deal to suspend the debt ceiling until expires in December and might require action after the New Year. (A White House official said that when it comes to the "biggest agenda item, tax reform, "the president, the majority leader and the rest of the Big Six are working very closely together and are in sync.")