Supreme Court rules man can't trademark 'Trump too small'

A man attempted to trademark the phrase 'Trump Too Small' for use on T-shirts and other merchandise. The government denied the request, a decision upheld by the justices, citing that the phrase could still be used but not trademarked without Trump's consent.

Why did government officials say the phrase could not be trademarked?

What was the government's stance on the use of the phrase without trademarking?