Ohio Sen. Rob Portman (R) will stump for Mitt Romney in Colorado this week, becoming the latest potential vice-presidential contender to hit the trail for the presumptive GOP nominee amid intensifying speculation over who Romney will choose as his running mate.

Portman will drop by a mobile phone bank in Johnstown, Colo., at 8:30 a.m. Mountain Time on Wednesday, according to the Romney campaign.

He will be joined by freshman Rep. Cory Gardner (R-Colo.), former congressman Bob Beauprez (R-Colo.) and Colorado Republican Party Chairman Ryan Call.

Portman, Call and Beauprez will then head to a 10:45 a.m. event at a campaign office in the town of Thornton, a 1 p.m. event in Lakewood, and a 2:55 p.m. event in the parking lot of Denver’s Mile High Stadium.

Portman and Call will then head to a final 7:05 p.m. event at a Pueblo campaign office.

The events come as another potential vice presidential nominee, former Minnesota governor Tim Pawlenty (R), visits Michigan to stump for Romney.

Pawlenty will attend an 11 a.m. office opening in Jackson, Mich. Then, at 3 p.m., he will stop by a campaign office in Portage, western Michigan, along with House Energy and Commerce Committee Chairman Fred Upton (R-Mich.).

The events are two of several appearances expected by the pair of vice-presidential hopefuls over the coming days. Pawlenty will visit New Hampshire for an ice cream social with state Republicans on Saturday, while Portman is expected to join Romney on the last day of his bus tour next Tuesday in Ohio.