What he meant by the title is that Trump was the first president to consciously and successfully wield "whiteness" as a tool to win the presidency. Using whiteness itself as an identity politic much in the way Hillary wielded the female vote and had she won been lauded as the first female president and Obama wielding the black vote and being lauded as the first Black president.
No president before Trump had to strategically wield whiteness as a tool to win the presidency. Past presidents won the presidency simply through "privilege" or "merit" in a system that was already comfortably white supremacist. Our current political climate is one in which white supremacy is waning, being threatened, and being poked at in all directions, so the fact that he was able to mobilize a base and win a presidency around the idea of "whiteness" is significant.
Reminded of what is described as the "tonal range" of white privilege by Margo Jefferson....
Caucasian privilege lounged and sauntered, draped itself casually about, turned vigilant and commanding, then cunning and devious. We marveled at its tonal range, its variety, its largesse in letting its humble share the pleasures of caste with its mighty.