It's been
argued against by people who claimed it would have been out of character for Reagan to do so. There's quite a bit of circumstantial evidence that the Regan Campaign DID, in fact, collude with the Iranian Government to prolong the hostage crisis until after the election. At the very least, the
Iranians believe that collusion took place, and they believe they were rewarded for it as arranged.
The only real question is to what extent Reagan HIMSELF was involved in that collusion or even knew about it. This is the same "I didn't know what my staff was doing!" defense used by Nixon, Bush Sr., and now Trump. It's the same defense Reagan used for Iran-Contra, first by letting his underlings take the blame for the deal and then pardoning every single one of them so they would never see jail time.
It is, however, extremely naive to think that none of these presidents even KNEW what their staff were doing, or that members of their campaigns would take such a radical step autonomously.
Nixon did indeed interfere with the Vietnam peace talks, but it is also highly unlikely that they would have been successful in time to make a difference in the 1968 election.
The
success of the peace talks was not a point of contention. It was the fact that the North
walked away from those talks that undermined LBJ's (and the Democrats by extension) ability to end the war on favorable terms. While a lot of Americans were willing to believe that the Vietnam War wasn't really worth the trouble of winning, getting the North to turn their backs on LBJ made it seem like they had gotten to that position in the first place because Johnson was a weakling that they couldn't respect.
And no, this is not a theory. The FBI actually caught them doing this, as LBJ is recorded as saying:
"I got one this morning that's pretty rough for you. Well, we have found that our friend, the Republican nominee, our California friend, has been playing on the outskirts with our enemies and our friends both, he's been doing it through rather subterranean sources here. And he has been saying to the allies that you gonna get sold out, you better not give away your liberties just a few hours before I can preserve it for you. Mrs Chennault is contacting their ambassador, this is not guesswork... Mrs. Chennault, she's young and attractive, she's a good lookin young girl, and she is uh, warning the South Vietnamese not to get pulled into this Johnson move."
Again: it's not a question of whether or not this actually happened. We KNOW the Vietnamese walked away because someone close to Nixon told them to and assured them that they wouldn't have to make as many concessions under Nixon. The only thing that is even slightly questionable is whether or not Nixon himself knew this was going on.