Jim Cramer thinks recent analyst downgrades on stocks with big runs will test investors.

"Right now, until the end of the year, I think we have one of those moments where you will have to work hard to keep your positions on and not to sell simply because of price," the "Mad Money" host said.

In the past, huge rallies have prompted investors to change disciplines midstream. Instead of selling the rips, they let the gains ride because the market blew through so many levels, the new levels would last.

This is a new environment, Cramer said. The days of toxic gridlock in Washington that prompted investors to sell stocks every time an issue arose and then buy them back when it was resolved could end.

Regardless of any political beliefs, Cramer said investors must accept that Republican rule could mean that more gets done in Washington, and the growth of the U.S. economy won't be bottled up by gridlock anymore.

"In this scenario, it's not business as usual. It is about being disciplined enough to stick around for a bigger payoff than we have had," Cramer said.

That doesn't mean investors shouldn't take profits on less-deserving stocks, or those that have gotten ahead of themselves that are pure commodity plays, he said. It simply means that right now the hardest thing might be to stay the course, rather than ring the register.

"Especially when taxes may be lower for stock sales in 2017, courtesy of Trump's pro-capital policies. It might have been the opposite under Hillary Clinton, and that is why you need courage to let your gains ride," Cramer said.

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