Former UN Ambassador Nikki Haley told NBC's "Today" on Tuesday that she never had any doubts about President Trump's truthfulness or fitness for office during her tenure.

"In every instance that I dealt with him, he was truthful, he listened and he was great to work with."

The big picture: Haley was promoting her new book "With All Due Respect," which recounts her time serving in the Trump administration and her work with other former Trump officials like Secretary of State Rex Tillerson and chief of staff John Kelly.

What she's saying:

On impeachment: "I have made up my mind. Impeachment is literally the worst punishment you can do to a public official. ... Impeachment is serious. It's the most serious thing you can do to a president. The other side of this is we are less than a year away from the election. Instead, let the people decide. Let them hear the testimony, that's fine, but let them decide."

"I have made up my mind. Impeachment is literally the worst punishment you can do to a public official. ... Impeachment is serious. It's the most serious thing you can do to a president. The other side of this is we are less than a year away from the election. Instead, let the people decide. Let them hear the testimony, that's fine, but let them decide." On the Ukraine investigation: "I think it's never a good practice for us to ask a foreign country to investigate an American. It’s just not a good practice. Having said that, there's no insistence on that call. There are no demands on that call. It is a conversation between two presidents that's casual in nature."

"I think it's never a good practice for us to ask a foreign country to investigate an American. It’s just not a good practice. Having said that, there's no insistence on that call. There are no demands on that call. It is a conversation between two presidents that's casual in nature." On Kelly and Tillerson: "I was a governor and if people in my Cabinet tried to undermine me, it's very dangerous. ... I didn't call them dangerous people. What I said is what they were trying to do is dangerous. I have always referred to John Kelly as a patriot ... but to undermine a president because you think you know better than him is wrong. It's wrong whether it's a Republican president or a Democrat president."

Go deeper: Nikki Haley says Rex Tillerson claimed people would die if Trump was unchecked