Yes, protectionist practices cross-border trade is One of the main factor in the forecasted slowdown in global economy growth. Time and again it has been brought through various media publications, including IMF, the World Bank and so on. It has clearly signaled that "Free Economy Cycle" has started reversing and that Protectionism and Regionalism is taking over in the present times.

I tend to agree with Eyal Ronen . Protectionism is not the cause of economic slowdown.

Let’s not forget the huge literature that was published on the return to ‘new normal’ after the 2008-2009 global crisis. The main points were that the 15 years period of high growth (roughly 1990-2005) had been an exception, mainly linked to the return of China into the World economy after decades and decades of absence. Another factor was the lack of growth-enhancing technical progress, at the difference of the post World-War2 30 glorious. The fear was that a return to protectionism as a (wrong) response to slow down and rising unemployment. Not the way round.

To conclude, if there is a causality (not sure, but ‘if’) protectionism is more the consequence of the economic slown down than the opposite. The roots of the slowdown have to be found somewhere else.

Post Scriptum:

This said, the US administration trade policy vis à vis China has nothing to do with trade, it is a political economy struggle to force a change in the Chinese industrial policy in its treatment of foreign direct investment and intellectual property.