Nixon, Watergate and Partisan Opinion. This topic comes up often enough these days that I think it worthwhile to lay out the facts in some detail in hopes of clarifying how partisans and the public at large reacted and when. /1 
Let's start with Nixon's approval by party over his entire term. Nixon was fairly popular through the first term, almost always over 50% approval, though hovering at or just below 50 for most of 1971. (Black line is overall approval) /2
To modern eyes the most striking fact is approval among Democrats is pretty strong: high 40s in 1969, around 40 in 1970, mid-30s in 1971, rising back to the 40s in 1972. Compare opposition party approval since 2005 has been about 10% /3
Republican approval held in the low-to-mid 80s until 1971, then dipped sightly to high 70s before rising to near 90% in run-up to 1972 reelection. (As was their practice, Gallup didn't poll approval during campaign, from 6/23-11/11/72) /4
The overlap between the overall line (black) and the independent line (purple) is fairly common in approval by partisanship, though currently independents are a bit below Trump's overall approval. /5
Had Nixon left office on Jan 29, 1973 he would have gone out with a very high 67% approval rating in the wake of a landslide reelection and the Paris Peace Accords, finally ending (or so we thought) the Vietnam war. /6
Nixon did not leave office, and the next 9 months showed one of the sharpest sustained declines in the history of presidential approval. dropping 4.1 points per month from late January to early October 1973, from 67% to 30% /7
Approval declined a little more but from January 1974 through August it remained in the 26-28% range until the last two Gallup polls of his presidency, both at 24% approval, the last taken 8/2-5/74. /8
So that is the overall story. Almost all the decline in Nixon's approval took place between February and early October 1973, a period of continuous damaging news stories about Watergate and a summer of televised Senate hearings. /9
By the time of the Saturday Night Massacre, on October 20, 1973, Nixon's approval had already reached its "steady state" low point, with almost no change until the bitter end. /10
The Massacre itself and subsequent revelations, including tape transcripts, and impeachment proceedings did little to reduce his approval ratings. Republican support remained about 54%, independents about 25% and Dems about 15%. /11
This last point deserves emphasis. The shocking Saturday Night Massacre, Nixon cited as an "unindicted co-conspirator", the release of tape transcripts that introduced "expletive deleted" to the lexicon barely moved opinion. /12
Note there is noise but possibly Republican approval declined slightly after the tape transcripts were released, to 50% or a shade higher. Independents and Dems don't seem to have been affected. /13
Nixon's resignation ended our job approval data. After the "smoking gun" transcript was released Aug 5 the 11 Republicans who voted against article 1 said they would now support the obstruction of justice article on the floor/14
It is probable that with the collapse of support from elected Republicans, approval of Nixon would have fallen below 50% among Republican partisans. /15
For reference, in the fall of 2008 during the financial crisis, Republican approval of President Bush ranged from 55 to 63, before rising after the election. /16
Nixon's approval collapsed between Feb and Oct 1973. Steady before, steady after. Revelations & evidence presented in those 9 months, not subsequent events, persuaded all who could be persuaded. \end
Addendum: Some economic trends during Nixon administration
