With the Presidential Election campaign beginning with the announcement of numerous Republicans having declared their candidacy or about to announce, an odd point to make is that ONLY one Republican Senator, Tim Scott of South Carolina, has announced his candidacy, and it is highly unlikely any other Republican Senators will join the fray.
Instead, the bulk of candidates are those who have served as Governors in the past or the present.
This includes Ron DeSantis (Florida), Nikki Haley (South Carolina), Mike Pence (Indiana), Asa Hutchinson (Arkansas), Doug Burgum (North Dakota), Kristi Noem (South Dakota), Chris Christie (New Jersey), Chris Sununu (New Hampshire), Glenn Youngkin (Virginia), and Greg Abbott (Texas).
In 2016, the following US Senators ran for the Republican Presidential nomination: Ted Cruz (Texas), Marco Rubio (Florida), Rand Paul (Kentucky), Rick Santorum (Pennsylvania), and Lindsey Graham (South Carolina). All except Santorum are still in the Senate, but not choosing to run this cycle!
There are also other Republican Senators rumored to have Presidential ambitions, including Rick Scott (Florida), Josh Hawley (Missouri), and Tom Cotton (Arkansas), but they have chosen to stay out of the race.