The candidates most widely discussed as replacements for Pence include Lt. Gov. Eric Holcomb, a former chairman of the Indiana Republican Party; U.S. Reps.
Pence has always been mentioned as a finalist on Trump's shortlist alongside Gov. Chris Christie (R-N.J.) and former Speaker Newt Gingrich (R-Ga.).
Merritt said he believes Pence will drop out of the governor's race come Friday: the deadline to withdraw.
Later, during a Facebook livestream, Gingrich said: "I told (Trump) quite directly that I thought he had a choice between having two pirates on the ticket or having a pirate and a relatively stable, more normal person". He's a more cautious, less-flashy choice over Gingrich and Christie. "That's going to help him in southern constituencies, like we have here in Texas".
"We'll find out what Donald Trump decides to do", he said.
Prior to serving as Indiana's governor, Pence served in the House of Representatives from 2001 to 2013.
Conservative radio host Steve Deace essentially makes the argument that Pence has lost so much allure, it's his only chance at a bigger platform. He was also president of a conservative think tank in the state, the Indiana Policy Review Foundation.
Trump did not specify when he plans to make the announcement. When he took office, the state's jobless rate was at 20 percent, per CNBC; it has now fallen to 5 percent.
Mark Joseph Stern, Slate: "Nationally, Pence is perhaps best known for signing into law a mean-spirited "religious liberty" bill targeting LGBTQ people - then revising the measure after its discriminatory goal sparked coast-to-coast outcry".
"I'm told he's been asked to do this and he's flying to NY", one source said. Despite the partisan leanings of his youth, Pence has remained a steadfast conservative for decades.
Presumptive Republican presidential nominee Donald Trump has postponed his pick for vice president because of the attack in France but all signs are pointing to Indiana Gov. Mike Pence.
If Pence is the choice, he will be called upon to rally conservative and evangelical voters behind the Republican Party's unorthodox candidate for president. Ted Cruz over Trump before Indiana's crucial early May primary - a contest Trump won, knocking Cruz from the contest and clinching the nomination.
Trump just recently left the Governor's mansion Wednesday after spending that morning with Pence and his family. Does it mean I am all ready to put on my engineer's cap and, woo-woo, get onboard the Trump train?
However, on Thursday, those at the top of the Republican establishment seemed to support Trump's selection even before the ticket was confirmed.
He also met with a fourth potential No. 2, U.S. Senator Jeff Sessions, 69, of Alabama, who has been one of Trump's closest advisers.
Republicans can replace him on the ballot.
This week has included a frenzy of meetings after Trump stayed in Indianapolis longer than originally planned.