It's not impeachment that will bring Trump down - it's the economy.
The only thing artificially inflating Trump's support right now is the perception the economy is doing well. It's why he's been able to essentially stay stable in his approval numbers despite being under investigation for the last two years. Trump is woefully under-performing the economy with his approval rating and that tells me he's a recession, or even a downturn, away from Bush-levels bad.
Trump's average approval today is 42.5%. It's been at this level for nearly a year - with only minor ebbs and flows.
The impeachment talk doesn't seem to ever change his numbers - good or bad.
The Mueller talk doesn't seem to to ever change his numbers - good or bad.
Barr's letter summarizing the Mueller Report was released on 3/24. On that day, Trump's approval was 43.6%. A week later, on March 31st, it was 43.5%. The redacted report was released on 4/18. On that day, Trump's approval was 43.9%. A week later, on 4/25, Trump's approval was 43.1%.
So...
3/24 (Barr Summary): 43.6%
3/31 (One Week Later): 43.5%
4/18 (Redacted Report Released): 43.9%
4/25 (One Week Later: 43.1%)
Today: 42.5
Trump's approval today is essentially one-point worse than it was the day the Barr Summary was released. It's literally a point worse than a week after its initial release and .6% worse than a week after the redacted report was released over a month ago.
That's some consistency.
Two things are clear here:
Trump was never able to win the narrative - despite his claim of being fully exonerated, his approval didn't see an uptick beyond outliers.
Trump was also not devastated by any of this - despite Democrats framing this issue as obstruction, Trump's approval has only gone down about a point. That's just noise.
Impeachment might drive this number down and make him politically toxic but what will unquestionably kill his second term chances, and even make him vulnerable to being removed from office, is if the the economy slides into a recession between now and this point next year. Then that 42% becomes his ceiling and his floor rivals Bush levels from 2007 and 2008.