Ken Fisher always says "that you should ignore politics in your investing."

I think it's generally good advice, but for completeness you really ought to add the word "usually". Or even "almost always".
Usually politics doesn't matter enough to business or investing outcomes to change what constitutes a good investment decision, and usually the headlines in the paper matter even less. But there are occasional exceptions.

I remember putting nearly half my investable net worth into Telmex just before the 1994 peso devaluation, for example. It did fine, measured in pesos!

For a small recent example, per this post... mungofitch writes on Recent returns ... all Americans on fixed salaries have had a pay cut of about 10% so far this year, and all those with US dollar cash or bond balances have just taken a ~10% haircut, as a US dollar buys less "stuff" than it did. Lots of local prices have also fallen in terms of their global purchasing power cost, at least for the time being, so the hit becomes visible only gradually. You get very different numbers with different starting dates, but the dollar buys less than at any time in the last 3 years, so it's a real loss.

Jim