A Senate insider has a dark warning about Mitch McConnell

Democrat Adam Jentleson can recite chapter and verse about Senate Majority Leader Mitch McConnell's bitter partisanship: he served as deputy chief of staff for former Senate Majority Leader Harry Reid during the Obama years. And in an interview with New York Magazine, Jentleson has a warning for President-elect Joe Biden: expect the worst from McConnell.

Jentleson discusses the state of the U.S. Senate in his upcoming book, "Kill Switch: The Rise of the Modern Senate and the Crippling of American Democracy." It remains to be seen whether McConnell will be Senate majority leader or Senate minority leader in 2021 — that will be determined by what happens in the two U.S. Senate runoff elections in Georgia in January. And when New York Magazine's Ben Jacobs asked Jentleson, during the interview, "how important" the outcome of those Senate races will be for Biden's incoming administration, he replied, "It's all the difference in the world."

Jentleson told Jacobs, "It is night and day. That ranges from prospects for passing legislation and having his nominees confirmed to who controls the committees and the day-to-day business and sets the agenda of the Senate. So, it's two seats that could lead to two very different prospects for Joe Biden when he is inaugurated in January."

The former Reid staff added, "If Democrats win those two seats, even though it's the barest majority possible…. that means that instead of Mitch McConnell deciding what bill is on the floor every single day, it will be Chuck Schumer in that decision seat. And it means that instead of Lindsey Graham or another Republican overseeing all of Biden's judicial picks, it will be a Democrat…. And that goes all the way down, from Supreme Court picks to circuit and district court picks. So, it is just a massive difference."

Biden and McConnell go way back. The 78-year-old president-elect served in the U.S. Senate from January 1973 to January 2009, when he was sworn in as President Barack Obama's vice president — and McConnell, who is also 78, was first elected to the Senate via Kentucky in 1984. McConnell has always been quite conservative, but in recent years, he has grown much more vindictive. For example, McConnell blocked many of Obama's judicial nominees and wouldn't even consider Obama's U.S. Supreme Court nominee, Judge Merrick Garland, in 2016. Obama was clearly willing to meet McConnell half way with the Garland nomination, proposing someone who was quite centrist in his judicial philosophy. But McConnell was determined to block anyone Obama nominated, however moderate.

When Jacobs asked Jentleson if it is a "given" that "McConnell and Senate Republicans are never negotiating in good faith," he responded, "Yes…. Even Republicans who demonstrate good faith in private are operating in a system that demands they toe the line of their base. Their base is not going to want to see them cut deals with Biden."

Jentleson warned, "I'm pretty pessimistic. I think that most of what Biden is going to want to get done is going to have to be done through executive action."