Why has Kamala Harris's approval rating spiked since she started running for president?

Kamala Harris saw her approval rating plummet in 2021, from around 50% when she first took office to the mid/high 30s, where it's hovered throughout most of her vice presidency. When she started running for president last month, her approval rating suddenly spiked to the mid 40s.

What's the reason for this improvement in her approval rating? What has she done other than becoming the Democrat nominee to explain this?

Edit: It would be especially interesting to hear from people who had a negative impression of her before she became the nominee but now have a positive impression.

https://www.realclearpolling.com/polls/favorability/kamala-harris