Judging by his four-year tenure as Speaker, Republicans could have plenty to worry about in 2012 if Newt Gingrich wins their party’s presidential nomination.

Even ardent Gingrich supporters concede he would begin a general election against President Barack Obama at a political disadvantage in terms of electability given his cemented image as a radioactive partisan. Other Republicans with fond memories of his 1995-1999 stint as Speaker acknowledge that the chaotic, undisciplined leadership style they experienced could present obstacles to winning the White House.

“Newt’s biggest deficiency is he lacks discipline,” said Sen. Richard Burr (R-N.C.), who served in the House when Gingrich was Speaker.

Gingrich as Speaker — and since then, some critics would argue — opined on any subject that struck his fancy, often changed directions after convincing the Republican Conference to support a particular political message, was viewed as a micromanager who had trouble delegating and who lacked organizational skills, and was tagged as arrogant, divisive and unlikable outside the GOP base. As a well-known public figure, Gingrich would have to work to undo this last definition in particular.

Republicans sympathetic to Gingrich downplay these charges as well as the notions that they helped sink his speakership prematurely or that they would be problematic if the Republican icon were to become president. But they do not deny the trouble such shortcomings could cause for Gingrich in a presidential campaign against the more disciplined Obama, who is expected to spend close to $1 billion to defeat the eventual Republican nominee.

“He has an opinion and thought on every issue and hasn’t yet learned how to not comment on every issue,” said a former senior aide to Gingrich. “He’s on top now, but I don’t expect him to stay there.”

Gingrich’s lack of discipline in his response to questions was on display early in his presidential bid, such as when he criticized the budget plan of tea party darling Rep. Paul Ryan (Wis.). And questions about his seriousness as a candidate were cited by staffers who left his campaign in droves in June in part because Gingrich decided to take a Mediterranean cruise with his wife instead of campaigning in key primary states, as his advisers had counseled.

Among the harshest critics of Gingrich’s speakership, and what it might portend for the GOP if he wins the nomination or the presidency, are Republican Members who served under him in the House. Although most credit him for engineering the House takeover in 1994 and subsequent legislative policy victories, they deride his leadership style as heavy-handed, hypocritical and damaging to the party over the long term.

Gingrich stepped down as Speaker after Republicans lost five seats in the 1998 midterms even as Clinton was embroiled in a sex scandal that led to his impeachment. Gingrich also received much of the blame for his handling of a budget fight that led to an extended government shutdown. Republicans who served with Gingrich have referred to him as occasionally disappointing as a leader and to his speakership as disorganized and inconsistent.

“I’m not inclined to be a supporter of Newt Gingrich’s, having served under him for four years and experienced, personally, his leadership,” Sen. Tom Coburn (R-Okla.) said in an interview on “Fox News Sunday.” “I found it lacking, often times.”

On Monday, Gingrich unveiled his first television ad of the campaign — targeting Iowa caucusgoers — while announcing a 50-state strategy to unseat Obama during a stop in New York to meet with businessman Donald Trump.

A 50-state approach might be ambitious for any presidential candidate — even for Romney, who polls the best against Obama in a hypothetical general election matchup, including among female voters and independents. But interviews with more than a half-dozen Republican operatives familiar with Gingrich’s 33-year Washington career, among them longtime fans supportive of his presidential bid, suggest that such a strategy is particularly unrealistic for the ex-Speaker.

“One of the last things he has left to prove is that he can win a general election and that it would be beneficial for the party to have him at the top of the ticket,” a Republican political strategist said. “Can he win women independents in suburban areas? I think he can — he represented a suburban district — but he’s going to have to prove that.”

The Gingrich campaign did not respond Monday to a request for comment. But longtime Gingrich backers defended the former Speaker, saying he has mellowed and matured with age since leaving office 13 years ago. They also argued that the 68-year-old deserves far more credit than he receives for what he achieved as Speaker, politically and for his executive leadership of the House.

These Republicans note that Gingrich took control of the chamber after Republicans had been in the minority for 40 years and constructed a team and systems to run the majority without the benefit of aides or committee chairmen with previous experience in charge. And Gingrich did more than develop conservative solutions to existing problems — an often-cited leadership quality — he built the bipartisan consensus needed to pass legislation and get it past President Bill Clinton’s veto pen.

“Newt gets sold short in terms of his tenure as Speaker and the skills he brought to the job,” said Dan Meyer, a partner at the Duberstein Group in Washington, D.C., who served as Gingrich’s chief of staff in 1995 and 1996. “He motivated people to be a part of something bigger than themselves; he had an agenda.”

Gingrich, since leaving office, has proved to be a savvy businessman with political staying power. He has been a prolific author and paid speaker, and until running for president he oversaw a web of profitable outfits engaged in conservative activism.

Gingrich — who has mostly lived in Northern Virginia since resigning his Georgia House seat in early 1999 — is surging in national and early state polls on the strength of support from tea party activists and grass-roots conservatives, with whom he has maintained strong, personal connections since leading Republicans to their 1994 House takeover.

Recent polls have shown the former 20-year Congressman ahead in Florida, Iowa and South Carolina and second to former Massachusetts Gov. Mitt Romney in New Hampshire.

Of course, Gingrich did not become the current favorite until others, such as Texas Gov. Rick Perry and businessman Herman Cain, flamed out after top-tier polling.