When Republicans are in power, Democrats may actually want the market to go down. They will predict it, and they will be ignored by the Republicans. When the market does crash, as it did in 2008, Republicans will quickly ascribe it to something nefarious done by Democrats. Most Republicans now blame what happened on Bill Clinton and federal mortgage insurance. That was the first step in a process leading to the crash, because it created a system that was open to abuse and manipulation. But it was not, in and of itself, abuse and manipulation. That’s a process that was ignored by the Bush people.
The same is very much true in reverse. Republican investors refuse to accept that the 2009 stimulus worked to jump-start the economy and that the GM bailout worked. They even deny that Republican efforts during that period were useful, including the bailout of Wall Street. They pretend that Ben Bernanke and Hank Paulson were Democrats in disguise. (Bernanke has since said he is no longer a Republican, but does not say he is a Democrat.)