Yep, it’s (largely) the economy stupid. I’d say that an early recession tends to better insulate a sitting president, though it also tends to damage the mid-term elections for that party. Think of Pres. Reagan’s first term, or the lesser Bush’s first term recessions. The recessions came early and the economy was improving well enough before the upcoming November elections. The 90-91 recession was over early enough for HW Bush, but after 12 years of Repugs in the WH, it was tough for a non-charismatic President to overcome party exhaustion. This economic expansion has been going now for about 8 years. Considering that post WWII, there have only been 2 longer expansions (the 1960’s almost 9 years; the 1990’s 10 years), I’d say the chances of clearly hitting a recession prior to November 2020 are fairly high. Most of the leading indicators people utilize only give a 6-month warning at best of a probable recession, so even 2018 isn’t out of the woods yet.
The problem though isn't Trump but Trumpism. Simply defeating Trump isn't enough. As long as he remains an inspirational figure for the right the problem of christo-fascism in America will remain.
The Christo-fascism affect should keep weakening at the presidential election level as states like Texas, Nevada, and Arizona (some examples) become more competitive due to increasing Hispanic population percentages.
Some fun numbers from Texas Presidential races are below. Don the Con couldn’t even do better than McCain, even though McCain was running during an obvious recession coming down our throat with 8 years of Repugs in charge:
2016: FFvC 52.23%
2012: Romney 57.17%
2008: McCain 55.39%