After the 2008 Sarah Palin debacle, Mitt Romney was understandably keen to pick a very different kind of vice-presidential running mate. Instead of a relatively inexperienced governor of an outlying state, in Paul Ryan the Republican presidential candidate has gone for a consummate political professional with 14 years of congressional experience under his belt.

But while Ryan is unlikely to have embarrassing, flustered moments in television studios when asked to list the daily newspapers he reads, he is proving every bit as controversial and polarising as his Alaskan predecessor.

The Democrats have dubbed him a "certifiably rightwing ideologue", claiming he is out to destroy America's modest welfare programmes.

Usually, vice-presidential candidates have only a few days in the media spotlight before retreating into obscurity, apart from one VP nationally televised debate in October. Palin did not follow that pattern and neither does Ryan, who after less than a week in the job has redefined the campaign and looks likely to go on doing so.

The Romney campaign chose him to deliver the Republican base vote amid fears that die-hard conservatives could cost him the White House by staying at home on election day rather than turning out for a candidate they are ambivalent about.

Conservatives are coming round, reflected in the crowds Ryan has been attracting on his tour of the swing states this week. The Democrats have been sending out panic-laden appeals for donations, one of them expressing concern over the size of the crowd. One of the appeals, for $3 or more, said of Romney-Ryan attacks: "This could cost us the election."

Charlie Gruschow, the Iowa-based founder of the Tea Party of America, said there had been a large crowd to see Ryan in Iowa. Gruschow is one of many conservatives who were slow to warm to Romney, having first supported Herman Cain and then Newt Gingrich as the Republican presidential candidate.

"Ryan has fired up the base," said Gruschow, after speaking to friends in the evangelical Christian community and the Tea Party who he said had been a little hesitant, a little concerned, about Romney. "I think now that Ryan has been selected as his running mate, there's a lot of enthusiasm. He is a Tea Party guy."