Can anyone beat Dianne Feinstein? A debate.

Cillizza: Maeve, let's do this!

DiFi announced on Monday that she's running for a sixth term. She will be 85 on Election Day 2018 and 91 if she serves her full term through 2024.

I will admit I was somewhat surprised that she decided to run again. What was the sense out in California? Were people surprised today? Or was it expected?

I've got a bunch more questions but let's start there!

Reston: I actually wasn't surprised, because we would have seen so much maneuvering among the younger generation of Democrats if Feinstein was actually sending signals that she was going to retire. There has been some frustration among younger Democrats here for years about the age of the party's leaders --- Feinstein, (Jerry) Brown, (Nancy) Pelosi, (Barbara) Boxer (before she retired and Kamala Harris won her seat). A lot of Dems here would have liked a shot at that Senate seat. But there's also deep respect for Feinstein, and the sense that she's not done yet in terms of the work she wants to do in the Senate.

Cillizza: That begs the next question: Will ANYONE step up and challenge DiFi? She's said some things -- Trump still has a chance to be a good president, etc. -- that make liberals crazed. And she's not the liberal crusader that Boxer was and Harris is.

Rep. Ro Khanna, who beat a Democratic incumbent in a primary in 2016, blasted Feinstein on Monday -- arguing that "there are other voices in our state who are far more in touch with the values" of California than the incumbent. Khanna is trying to recruit his colleague Barbara Lee -- one of the most liberal House members in the country -- to run. State Senate President Kevin de Leon has been talking up the possibility of primarying Feinstein for months now.

I'm skeptical that a House member or even a state Senator (fun fact: California state senators represent more people than California US House members) could possibly put together the money and organization you need to run and win in California. Feinstein is well known and personally wealthy -- a tough two-step for any challenger to match.

BUT. California is full of really rich liberals. Businessmen. Tech types. Maybe even a statewide elected official or two? So why wouldn't one of them take their shot against Feinstein who is in a tougher spot with Democrats than she's ever been before?

Reston: At the end of the day, the most serious potential primary challenger would be de Leon. But it's hard to see why he would do that other than to raise his name ID, which is quite low in California beyond political circles. He is very ambitious and term-limited, and in the age of Trump, he's been quite good at getting on television to challenge the administration.

Sources tell me he was doing polling in a number of different statewide offices as he considered his options this year. But the governor's race is already packed with Lt. Gov. Gavin Newsom and former LA Mayor Antonio Villaraigosa. And in a competitive Senate race in California, you have to raise well over $25 million just to get on television in a real way. There's no indication that he has that kind of donor base; and from a fundraising perspective alone, it wouldn't make much sense to go up against a wealthy candidate like Feinstein.

Remember that even though you have a lot of progressive Democrats making noise, her job approval rating is still 54% according to the most recent PPIC poll. That is quite good. (Brown is at 55% and there are lot of senators running for re-election around the country who would like to see numbers that strong). In every race, Feinstein has run strong in the Democratic base. She has a huge base in Northern California, and she's never lost Los Angeles County in any race.

In terms of wealthy Silicon Valley/entrepreneur types, everyone always looks at Tom Steyer as a potential challenger, because he's been so active in Democratic causes. He wouldn't rule out running against Feinstein earlier this year, but he seemed more interested in the Governor's race -- and his main advantage in other races has been his wealth (which wouldn't make a difference here). So taking on Feinstein seems unlikely.

At the end of the day, no one knows exactly what de Leon will do, but mounting a challenge against Feinstein could well end up being a quixotic exercise for him. Beyond that everyone who has filed to run against her is unknown. So it doesn't seem like Feinstein has much to worry about at this point.

Cillizza: OK, last thing. Let's assume Feinstein wins the primary and the general election. What's her legacy -- in California politics and in Democratic politics more generally?

She was always talked about as a potential presidential candidate but never ran. She has held virtually every senior committee position possible in Washington. Her career began amid a very high profile political tragedy.

So, what can we say about her? What has she meant?

Reston: Clearly she will always be defined by her unwavering, decades-long fight for tighter gun control measures, including the assault weapons ban. She has long recounted how she became San Francisco's mayor "as a product of assassination" when she found the body of San Francisco Supervisor Harvey Milk --- and "put her finger through a bullet hole trying to get a pulse," she said --- after the 1978 shootings at City Hall. She has not succeeded in achieving what she set out to do on gun control, but she was one of the most effective advocates for that viewpoint.

She also represents that last generation of senators who were defined by their embrace of bipartisanship and statesmanship. She was widely admired by her colleagues as the chair of the Intelligence Committee and her dogged probe into the CIA's detention and interrogation techniques after the September 11 attacks. She has embodied that put-your-head-down-and-work ethos of the Senate, praised by colleagues on the other side of the aisle for her fairness and thoroughness. That's a rarity in the polarized era of Trump.