Republican U.S. presidential candidate Mitt Romney (R) stands with his vice president selection U.S. Congressman Paul Ryan (R-WI) and granddaughter Chloe while speaking to the press aboard a charter flight to Charlotte, North Carolina from Dulles Airport August 11, 2012. [Photo/Agencies]

It is likely to add excitement for the conservatives who make up the party's core and will be out in force at the Republican National Convention - where Romney will officially be named the party's presidential nominee - in Tampa, Florida, in the last week of this month.

"We are offering a positive, governing agenda that will lead to economic growth, to widespread and shared prosperity, and that will improve the lives of our fellow citizens," Romney said.

The announcement thrilled conservatives whose Midwestern home state favors the Democrats but which could now be in play with a native son on the ticket.

"This is excellent news. I'm excited. I'm in tears," said Joanne Terry, a Tea Party organizer in Ozaukee County, north of Milwaukee. "Weighing the options, he (Romney) was the best, but now with Ryan, he is definitely the best."

South Carolina-based Republican strategist Adam Temple said the choice of Ryan suggests Romney is thinking beyond November.

"Any choice Mitt Romney had to make carried risks, but the reward is greater in this case. Paul Ryan has a clear understanding of the economy and how to improve it, one of Mitt Romney's top priorities, and they both have demonstrated chemistry on the campaign trail," he said.

Forming a Team

Romney and Ryan bonded during the Republican primary battle in Wisconsin last spring when Ryan enthusiastically campaigned with the 65-year-old candidate.

But their personal chemistry does not mean Romney endorses all aspects of the Ryan budget, Romney aides said.

Ryan began work on a budget blueprint of his own before Republicans captured the House in the 2010 mid-term elections, but it got little attention from Republican colleagues, who were not interested in associating themselves with a detailed list of budget cuts.

By the fall of 2010, however, the budget - and the deficit - had become defining issues, in part due to the Tea Party.

After Republicans took control of the House in January 2011, Ryan became chairman of the House Budget Committee. Suddenly he was one of the Republican Party's most visible leaders, and a frequent guest on cable news.

Ryan's budget plan passed the Republican-controlled House of Representatives last March, despite significant Democratic opposition. It went nowhere in the Democrat-led Senate.

There has been some tension between Ryan and Federal Reserve Chairman Ben Bernanke. Ryan has been critical of Fed policies that he says have, among other things, created a false sense of security about the economy and contributing to the real estate crash and financial crisis.