A tipoff came a few days ago when Indiana House Speaker Brian C. Bosma, 58, a conservative Republican, sought advice on running for governor from constitutional lawyer James Bopp, an Indiana delegate to the Republican National Convention and a member of the convention rule committee.
“He wanted my counsel on what he needed to do to set himself up to run for governor, because he expects Pence to step down as governor in order to be Trump’s running mate,” Mr. Bopp said in an interview.
Mr. Pence also made a telling private call to Indiana Republican Party Chairman Jeff Cardwell, a Republican close to both men said.
In the call, the governor told Mr. Cardwell to delay his planned Tuesday departure to Cleveland for a Republican National Committee meeting, saying Mr. Cardwell needed to be sure to attend an Indianapolis fundraiser featuring Mr. Trump and Mr. Pence.
The Trump election team on Sunday announced a campaign rally in Indianapolis following the Trump-Pence fundraiser, giving further weight to the expectation that the presumptive nominee will announce Mr. Pence as his running mate — most probably at the rally.