There is a reason that reasonable people don't use the term 'radical Islam'. It is because this is just another dog whistle to the small but energetic group of people who want to believe that Muslims are terrorists. Not that, this or that Muslim was or is a terrorist, but Muslims are terrorists.
That is why Republicans are not really upset that the left refuses to use the whistle, because they count on the effect it has on this small but very energized group, not only when they use it but when Obama refuses to. That group has kept the extreme right in power for the last few years.
The key characteristic of this angry few is that they show up to vote and they vote Republican.
The dog whistles work. You call any young black man shot down, a thug, because young black men are very scary to them and represent a menace. The anti gay movement, again a small group by count, but they get out and vote. And radical Islamist … Muslims are trying to kill us and take over America. And Mexicans, this applies to any Latino because Mexicans are pouring over our boarders to rape our women and take over America.
Then the most effective dog whistle “Take America back”. Back to when all of these scary people weren't here menacing us. They easily discount that the America they want back is nothing like their fantasies because that is not the point. The point is it seems so clean and simple. Just like the old black and white TV shows where black was just another color on the white people. Everyone else was a bit player, a simpleton or foreign.
Trump and republicans in general know where their vote comes from. They are not worried about minorities. Where there is any number likely to vote there are strong voter repression laws in place to tamp that down. They certainly aren't worried about progressive Democrats because they run and hide when they don't get their way and vote in very small numbers.
The term “radical Islam” is a call to voters, voters that will show up and they will vote for Trump and that is guaranteed.
Should you be afraid …. ??