Could Mitt Romney’s vice-presidential announcement come before the end of the week?

With Romney’s Friday schedule yet to be announced, some campaign watchers were speculating that the presumptive Republican nominee could declare his choice just ahead of this weekend’s start of a four-day bus tour.

That would appear to be the earliest date for a decision. His wife, Ann Romney, has been in London this week, having stayed behind after his European trip to watch a horse part owned by the couple compete in the Olympic dressage event. The horse, Rafalca, on Tuesday failed to achieve a high enough score to remain in medal contention.

A vice-presidential announcement in the lead-up to Romney’s swing-state bus tour could make for some awkward optics, however. Romney will be joined at points along the trip by several top Republicans thought to be on his shortlist, including Sen. Rob Portman of Ohio, Sen. Marco Rubio of Florida and Virginia Gov. Robert F. McDonnell, who will team up with Romney on Saturday in the Old Dominion.

Romney has sought as much leeway as possible. He told Fox News that the selection of certain people for speaking roles at the Republican National Convention in Tampa doesn’t necessarily rule them out of the vice-presidential race. And about the timing of the announcement, he has said only that it will come before the third night of the Aug 27-30 convention, the spot traditionally reserved for the vice-presidential nominee’s speech.

On Wednesday, several of the Republicans thought to be on Romney’s short­list were busy proving their mettle on the campaign trail.

Portman headlined a five-stop bus tour that is shadowing President Obama in Colorado, spending a nearly 12-hour day on the trail in a key battleground state.

“Guess what’s going to welcome President Obama to Colorado today?” Portman asked a crowd of about 50 supporters at his first campaign stop of the day in Johnston, Colo., according to ABC News. “Some new polls that show Romney up. They’ve outspent us, but they can’t outwork us because of people like you.”

Louisiana Gov. Bobby Jindal (R) will be in Colorado stumping for Romney on Thursday. Former Minnesota governor Tim Pawlenty (R), meanwhile, headlined two events for Romney in Michigan on Wednesday.

The campaign stops marked the beginning of a busy few days for the rumored vice-presidential shortlisters.

On Friday and Saturday, Pawlenty will be in New Hampshire headlining four events, including an ice cream social with state Republicans in Manchester. Portman is expected to join Romney next Tuesday on the final leg of his four-state bus tour.

Another reported finalist in the race for the No. 2 spot, House Budget Committee Chairman Paul Ryan (R-Wis.), will be taking a little time off the trail: Ryan plans to take a week-long vacation in Colorado with his family starting Saturday.

With a potentially life-changing announcement set to be made in the next several weeks, those reportedly on Romney’s shortlist have maintained that they aren’t giving much thought to the vice-presidential process.

“We’ll know soon enough,” Pawlenty said when asked Wednesday whether he plans to return to Michigan as vice president, according to ABC News.