Already hearing rumblings from the potential candidates on who wants to take P. Trumps job when 2028 rolls around. Some interesting, some just long shots with no hope. Both parties will likely see very crowded fields.
Republican
Ted Cruz
Ran in 2016, and has stated he intends to "Run sometime in the future".

Ron DeSantis
Has expressed interest. Considered a strong challenger.

Tulsi Gabbard
Seems to be a wild card. Former DNC Chair and representative from Hawaii. Her flipping to the GOP and becoming the DNI have many thinking this will serve as a launching board for a run as a Rep.

Nikki Haley
Many believe she's not done yet after how well she did in '24.

Kristi Noem
Head of Homeland Security. Leading the charge of dealing with the illegal immigration problem. She considered running in '24 but decided not too. Many speculate she will once Trump is out of office.

Marco Rubio
Current Sec of State. Ran in '16. Has given many hints at a possible run.

Tim Scott
Ran in '24. Many speculate he will run again.

Donald Trump Jr.
A fair amount of gossip on his future. Many speculate he may follow his father into the WH. Everyone is watching his moves over the next few years.

JD Vance
Tradition typically says the VP often is the next to run. How he preforms as VP will decide his future.
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Out of these potentials, personally Tulsi Gabbard & Kristi Noem could perform well if they fill their current jobs well and handle the next 4 years of attacks from the left. But top runners have to be Ron DeSantis & JD Vance with honorable mention to Rubio. A wild card will come from Trump Jr. if he does run with his father's backing, could once more dominate the field.
Democratic 
Cory Booker
Ran in '20. Very quite during Biden's term. Has recently started making noise to the Media once more. A strong indication he intends to run.

Pete Buttigieg
Ran in '20. Won the Iowa Caucus. His tenure of the Dept. of Transportation, had the official DOT page reading like a Buttigieg for President page.
Kamala Harris
Her loss still has many thinking the election was stolen from her due to factors beyond her control and if she ran again she would win. She has given every indication she will run again. Watch her come '26. She may run for Cal. Gov.

Amy Klobuchar
Ran in '20. Had considered a '24 run, currently hinting at a '28 run.

Gavin Newsom
Considered up till the recent disasters in Cal as the parties front runner. He in '24 was laying the ground work for a '28 run.

Alexandria Ocasio-Cortez
She has shown strong ambitions at not only unseating Pelosi and becoming the leader of the Dem party in the House. She has also stated interest in running for higher office.

Josh Shapiro
Considered by many as a strong contender. Many top movers in the DNC (Including B. Obama) are swooning him for a potential run.

Tim Walz
Many of Harris's staffers have said "six months ago, Walz's name wouldn't have been on the list, now it might be on the top." He believes their run was stolen.

Gretchen Whitmer
At one time, she was considered a running mate for Biden in '20. She has shown a massive increase in media coverage. A good indication of a pending run.
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Far as the dems go, my personal views, Harris and Pete will run but both will do worse. Harris is only a fav right now do to her recent loss. Jose Shapiro will do well in the NE area, but being a Jew, he will fail to do well in Wis, Min and Mi. AOC should she run will do well with young voters, but drop humiliated when the party''s true colors show. The top two look to be Newsom and Whitmer. Both have their issues. But should Newsom handle Cal disasters he could clench it. Whitmer will do well in the NE area.