Who will replace Orrin Hatch in the Presidential Line of Succession?

This might turn out to actually matter, if Paul Ryan (because of his own Russia dealings) and Mike Pence get dragged into the coming scandal.

Present line of succession
No. Office Current officer
1 Vice President Mike Pence (R)
2 Speaker of the House of Representatives Paul Ryan (R)
3 President pro tempore of the Senate Orrin Hatch (R)
4 Secretary of State Rex Tillerson (R)



UPDATE:

It's Thad Cochran, R-Miss -- but there is already speculation that he might be resigning because of poor health, so Grassley might be the next President pro tempore.

https://www.washingtonpost.com/powerpost/orrin-hatch-announces-he-will-retire-from-the-senate/2018/01/02/e76434c4-eff0-11e7-97bf-bba379b809ab_story.html?utm_term=.a34b2c0c695a

Hatch will also give up the title of president pro tempore, the constitutional leader of the Senate who is in the presidential line of succession behind the vice president and House speaker. If Republicans hold the majority, Sens. Thad Cochran (R-Miss.) and then Grassley are next in line to claim that largely honorary role.


https://www.politico.com/story/2017/12/21/mississippi-senate-thad-cochran-future-in-doubt-308157

Sen. Thad Cochran, chairman of the powerful Appropriations Committee, hasn’t presided over a hearing since early September. The Mississippi Republican has not given a speech on the Senate floor all year, and he’s introduced only two bills during that time, both of them minor.

To the extent that Cochran weighs in on any issue, it's in the form of an official statement from his office or the appropriations panel. He has stopped meeting with anyone about substantive committee business, including other senators or House members, according to several sources familiar with his activities. Cochran’s aides deny this is the case.

The 80-year-old’s feeble performance has fueled expectations — among senators and aides who’ve witnessed his physical and mental decline firsthand — that Cochran will step down from the Appropriations chairmanship early next year, or resign from the Senate altogether.

“The understanding is that he will leave after Jan. 1,” said a Republican senator who serves on the Appropriations Committee. “That’s what most of us believe will happen.”