If by that you mean he was planted or offered up by Kennedy, I think there is no evidence for that. If you mean Kennedy was watching McCarthy closely to see what opportunities might exist for his own candidacy, undoubtedly this was the case.
There was a sizeable right wing of the Democratic Party, and a sizeable left wing of the Republican Party; which for one thing made a win for one less terrifying for people who preferred the other, and for another meant that there were a lot more viewpoints within the parties which might stand some chance of being nominated. Especially since the nomination was still done at the conventions – these days the conventions are just a big shindig celebrating whoever was nominated earlier.
Yeah, I don’t think so either.
There probably are people who would poll as well or better against Trump. But I think any of them would have to be pried out of the woodwork by force to get them to run. And I don’t know who they are. And I am pretty sure that there are lots of Democrats who would poll worse than Biden against Trump.

There probably are people who would poll as well or better against Trump. But I think any of them would have to be pried out of the woodwork by force to get them to run. And I don’t know who they are. And I am pretty sure that there are lots of Democrats who would poll worse than Biden against Trump.
The only one I can think of, Michelle Obama, has stated in no uncertain terms that she’s not interested. I can’t think of anyone else either. Gavin Newsom is the only other name that pops into my head that’s even close, and I’d bet he would do worse than Biden.
If 2024 was more like 1968 somebody would already have set 1211 Avenue of the Americas in Midtown Manhattan on fire, followed by widespread riots.
Now why so many US-Americans seem to want to be deluded or at least say so in the polls, I have no clue. Concerning the NYT article that probably gave rise to the OP’s question (here is a gift link) the answers the people quoted give when asked why they would vote for Trump despite being traditional Dem voters are incomprehensible to me. Incomprehensible like making me want to grab them by the sleeves, shake them and shout: HOW STUPID CAN YOU BE?

Klobuchar, Harris, Buttigieg, O’Rourke, Castro
And how many of those caught fire with the voters? And would do better than an incumbent president, against a candidate who is polling strongly?
Hey hey
LBJ
How many kids
Did you kill today?
Biden doesn’t have this kind of baggage.
Yep, that was it.
Putting my QOP hat on…
Of course not! Sleepy Joe just rapes children, Hitlery murders them.

the answers the people quoted give when asked why they would vote for Trump despite being traditional Dem voters are incomprehensible to me. Incomprehensible like making me want to grab them by the sleeves, shake them and shout: HOW STUPID CAN YOU BE?
Exactly. So, my response to this is that if our nominee is so unattractive that people are behaving irrationally rather than vote for him – maybe its time to consider a different candidate.
I rather think that it was also that LBJ was, with part of his mind, thinking the exact same thing. Every night, when he tried to get to sleep. (Which was, of course, rather the point of the chant. But some people wouldn’t be vulnerable to it.)
It’s a hell of a job, whether one’s doing it right or wrong. I think he decided he couldn’t stand to do it any longer.

So, my response to this is that if our nominee is so unattractive that people are behaving irrationally rather than vote for him – maybe its time to consider a different candidate.
I don’t think they’re behaving irrationally because of Biden. I think they’re behaving irrationally because of Trump. I don’t know what it is about Trump that works on some people; and it certainly doesn’t work on me; but whatever it is, it’s powerful.

Exactly. So, my response to this is that if our nominee is so unattractive that people are behaving irrationally rather than vote for him – maybe its time to consider a different candidate
Polls this early still aren’t worth much. I seem to recall a time a year ahead when Rudy Giuliani was #1 in the polls for the Republicans.

[…] if our nominee is so unattractive that people are behaving irrationally rather than vote for him – maybe its time to consider a different candidate.
I think it would help to team up with a different vice-president on the ticket. Republicans have it too easy to paint Kamala Harris as the one who is being voted president (because Biden is so old, you know, that he won’t last long anyway and so on and so forth) and are painting her as a mix of what they hated most in Obama (skin colour, mostly) and Hillary (female) with some success. It is mean, dastardly and shabby, but it seems to be working. It worked the last time Trump won. That is what it looks like from afar, at least.
I realize that this would be playing their game, but I still think it would help.
I may be wrong on both counts, of course.
ETA:

I don’t think they’re behaving irrationally because of Biden. I think they’re behaving irrationally because of Trump.
Yes, that too.

Exactly. So, my response to this is that if our nominee is so unattractive that people are behaving irrationally rather than vote for him – maybe its time to consider a different candidate.
No. It just means he needs to do a better job at campaigning. He’s doing fine at presidenting.
Eventually I could see Hakeem Jeffries running, but I don’t know who we’d pick right now.

So, my response to this is that if our nominee is so unattractive that people are behaving irrationally rather than vote for him – maybe its time to consider a different candidate.
If they’re willing to vote for Trump, there isn’t anyone that the Democrats can offer. Trump is as old as Biden, and the inflation problem started under his watch. Inflation has stabilized under Biden now. So they must be attracted to what Trump represents. And Democrats are not going to allow a Trump-alike run for them.
But I still say the biggest counterargument has already been stated. The Democrats lost in 1968. Their strategy of kicking out the incumbent was a losing one. Why would they want to repeat that?
The only reason to try that strategy again would be if the incumbent was doing far worse than LBJ was. And Biden is liked more, not less.
I am hoping that Robert Caro and I both live long enough for him to get his massive multi-volume page-turner biography of a Lyndon Johnson up to 1968, and for me to read it. Then I will be able to better answer this thread question.
However — in every single month of 1967, 1968, and 1969, over 400 American troops died in Vietnam. In that sense, I expect and very much hope 2024 will not be like 1968.
Biden must feel an enormous weight on his shoulders over the twenty estimated American Hamas hostages, whose families he has talked to personally, and will talk to again regardless of outcome. But the pressure on Johnson was another order of magnitude.

I don’t know what it is about Trump that works on some people; and it certainly doesn’t work on me; but whatever it is, it’s powerful.
I can tell you exactly what it is. Individual-ONE is an outsider, not part of the establishment. The Gospel According to Saint Ronnie 2:80 says “Government BAD!”, and Individual-ONE is one to come in an clean it up. This R narrative has been pounded so ceaselessly that reasonable people have come to accept it, and it is not helped by that guy down at the planning office who refuses to let me build a concert stage in my own back yard, I mean, who is that going to hurt, freedom!
In fact, there may even be nitilists on the left who will facilitate the election of the Rs (if by not voting or by voting third-party) because they want us all to see just how bad those people on the right can make things.
And in fact, it cannot be denied that government has some serious defects that need to be fixed. So we should take the Republican approach, which is akin to fixed the fuel injection system with a sledgehammer (preferably one with Wagner Group inscribed on its head).
There is no one in the political landscape right now who is as electrifying as Robert F. Kennedy, Jr. was in 1968 (no, not even Trump.) Not only because of his personal magnetism, but because he was the embodiment of the Kennedy legacy, before that legacy became more tarnished under the view of history.)
Johnson also knew that millions of voters weren’t all that fond of the Civil Rights Act of 1964 (although whether he actually said the Democrats had lost the South “for a generation” is up for argument).
If there were a prominent Democrat as charismatic RFK, if Biden believed he personally would be held responsible for a massive change in the white power structure, and, frankly, if Biden were as concerned about dying in office as Johnson was (he died just two days after his second term would have ended) then we could ask why 2024 isn’t more like 1968.

There is no one in the political landscape right now who is as electrifying as Robert F. Kennedy, Jr. was in 1968 (no, not even Trump.)
RFK Senior.
Shame that family really sucks at naming their scions distinctively.