It will cost him some of his remaining support among the MAGA faithful. Some of them are just in love with Trump, or at least with the image Trump presents. Some are in love with Trump's (stated) policies, like "America first" and "no new wars".
And even of those who are in love with Trump's image, this may tarnish the image enough for some of them to fall out of love with it.
It won't cost him all of MAGA. But it will cost him some.