What's the lowest possible approval rating Trump can have, and still win?

[Ronnie]

Here's the scenario: let's say Democrats put up the worst possible candidate in your mind, out of the people who might reasonably run.  For some of you, this candidate might be Cory Booker, and for others, it might be Martin O'Malley, Andrew Cuomo, or someone else entirely.  What's the lowest approval rating Trump can possibly have, and still pull off a win against this hypothetical horrible candidate?

[GlobeSoc]

~35-40%, but it would take an even more perfect storm than 2016 ever was. Anything lower than that and a victory for him would probably require the Democrat to be a literal demon.

[Technocracy Timmy]

Is it a fair and free election?

[Ronnie]

Is it a fair and free election?

Well, it depends on how you define "free and fair".  But in terms of vote-counting, I suppose it wouldn't be any different than 2016.

[SWE]

Is it a fair and free election?

Almost certainly not.

[pbrower2a]

43.5%, according to a model that I have adopted from Nate Silver for incumbent Governors and Senators. An elected Governor or Senator usually gains about 6.5% from his approval rating to his share of a binary election (ignore third-party and independent alternatives) just by campaigning against an average challenger under normal conditions. I am guessing that much the same holds for a President as for an elected Governor or Senator, the usual last office that most newly-elected presidents have held.     

[twenty42]

Bush's approval ratings were in the 40's leading up to the 2004 election, correct?

His national approval rating won't mean much. If he can hold on to PA and FL, he will very likely be reelected.

[I Won - Get Over It]

All Adults:
~37-40% if Democrats choose a pro-establishment or/and "Identity Politics" candidate.

~43-45% otherwise.

[Liberalrocks]

Is it a fair and free election?

Well, it depends on how you define "free and fair".  But in terms of vote-counting, I suppose it wouldn't be any different than 2016.

Well 2016 was NOT a fair and free election considering a foreign government had influence so I guess this answer can be interpreted as NO.

[Ronnie]

Is it a fair and free election?

Well, it depends on how you define "free and fair".  But in terms of vote-counting, I suppose it wouldn't be any different than 2016.

Well 2016 was NOT a fair and free election considering a foreign government had influence so I guess this answer can be interpreted as NO.

There is no reason to believe Russia influenced the vote-counting process.

[Bojack Horseman]

Honestly I think it could be a 1% approval rating and he'd still have a chance. His supporters are like a cult; they literally would drink the Kool-Aid if he told them to. The deplorables will still turn out in droves in 2020, we just have to hope that the Indies have been thoroughly disgusted by this dumpster fire of an administration and vote for whoever we end up nominating.

[Santander]

Is it a fair and free election?

Hopefully not.

[Maxwell]

33%. It's enough to where if Democrats nominate a weak candidate, there would be enough begrudging Republican support and people voting third party for Trump to weasel in with 44-45% of the vote again.

[Inmate Trump]

Honestly I think it could be a 1% approval rating and he'd still have a chance. His supporters are like a cult; they literally would drink the Kool-Aid if he told them to. The deplorables will still turn out in droves in 2020, we just have to hope that the Indies have been thoroughly disgusted by this dumpster fire of an administration and vote for whoever we end up nominating.

This.

And to other Dems who couldn't bring themselves to vote for Clinton, for whatever reason, you are partly to blame for what we're dealing with now.

[Rjjr77]

I havent run the math, but a cursory guess would be somewhere around 35%

[Crumpets]

Here are the numbers for all presidents since Truman at the point of their reelection campaign, using Gallup for all but 2012, which uses RCP:

Truman - 40% Approval, 49.6% PV, 52.4 Binary, Won
Eisenhower - 70% Approval, 57.4% PV, 57.7 Binary, Won
Johnson - 74% Approval, 61.1% PV, 61.3 Binary, Won
Nixon - 56% Approval, 60.7% PV, 61.8 Binary, Won
Ford - 45% Approval, 48.0% PV, 48.9% Binary, Lost
Carter - 37% Approval, 41.0% PV, 44.7% Binary, Lost
Reagan - 58% Approval, 58.8% PV, 59.2% Binary, Won
Bush - 34% Approval, 37.5% PV, 46.5% Binary, Lost
Clinton - 54% Approval, 49.2% PV, 54.7% Binary, Won
Bush - 48% Approval, 50.7% PV, 51.2% Binary, Won
Obama - 50.1% Approval, 51.1% PV, 52.0% Binary, Won

Difference PV-Approval
Truman +9.6%
Eisenhower -12.6%
Johnson -12.9%
Nixon +4.7
Ford +3.0%
Reagan +0.8%
Bush +3.5%
Clinton -4.8%
Bush +2.7%
Carter +4.0%
Obama +1.0%
Average: -0.1
Average Post-1970: +1.9%

Difference Binary-Approval
Truman +12.4
Eisenhower -12.3
Johnson -12.7
Nixon +5.8
Ford +3.9
Carter +7.7
Reagan +1.2
Bush +12.5
Clinton +0.7
Bush +3.2
Obama +1.9
Average: +2.2
Average Post-1970: +3.9

In my opinion, Trump will need at least 47% of the binary, and at least roughly 45% of the PV to get elected, although the latter will depend entirely on third-party numbers. Using the overall "average" of the above numbers, that means 45% is a pretty good guess. Going by just the post-1970 numbers, he could be as low as 43% and still have a realistic shot. Anything below that and he is a very clear underdog.

[ShamDam]

I agree with pbro that Trump's approval rating will not necessarily be predictive of the election result, especially if the Democratic candidate has low favorables again