If Karl Rove’s involvement in the outing of undercover CIA agent Valerie Plame Wilson ultimately forces him out of the White House, what will President Bush do without the political guru he calls “boy genius” on good days — but “turd blossom” in tough times?

A lot rides on the answer to this question, both for the president and his party. Rove’s legendary skills at political tactics and message management could prove to be as indispensable in the remaining three and a half years of Bush’s presidency as they were in getting him to the White House in the first place.

For starters, Rove would be needed for the escalating ideological battle over judicial nominations, the never-ending need to spin the Iraq war as favorably as possible and the imperative to keep wobbly Capitol Hill Republicans in line for Bush’s shaky domestic agenda.

In short, Rove is Bush’s hatchet man — the tough guy who berates wandering believers and bullies the opposition to the sidelines. But even more than that, Rove is an unusual combination of policy wonk and political mechanic, the guy who ties it all together for Republican power players.

1. The Vision Thing. Bush’s dream of remaking Social Security will hardly have a chance, if it ever does, without Rove. Above all others in the White House, it is Rove who most passionately articulates the “reform” legacy that he and Bush are pursuing with this proposal: Rove dubs it a crusade to update federal programs that “were created for the world of yesterday, not for tomorrow.” Blending broad policy themes into the hard-knocks world of grass-roots politics is Rove’s trademark. His relentless advice to GOP candidates, including his boss, on how to make the war on terrorism a lethal campaign weapon once prompted a friend of then-Secretary of State Colin L. Powell’s to teasingly ask, “Who runs foreign policy, you or Rove?”

2. The Simple Difference. Rove’s word for what he does for Bush is “heuristics.” In a Time magazine profile last year he described this as providing Bush with shortcuts for “explaining something complex,” or, as he more precisely defined his role, “explaining away something complex.” Winning the Supreme Court vacancy battle ahead would test Rove’s skills in this regard, as the president will surely have to defend his pick with sharp-edged rhetorical firepower in a mind-numbing realm of legal jargon.

3. Message Enforcement. The closer Bush gets to being a lame duck, the more he might need Rove’s hand in keeping other Republicans from straying to their own agendas. Christine Todd Whitman offers a telling story about Rove in her book, “It’s My Party Too.” Following Whitman’s first meeting with Bush after he picked her to run the EPA in late 2000, Rove took her aside and said she would be one of just three Cabinet-level officers who would help determine whether the president would be re-elected four years later. She thought this meant that Rove wanted a pro-environmental record for attracting moderate voters. But after getting fired for being too cushy with environmentalists, she conceded in her book that “I don’t seem to have understood Karl correctly.” Rove wanted to appeal to the conservative base by pulling back on environmental regulations, she concluded.

4. The Politics of Subtraction. As GOP mavericks and moderates, such Sen. John McCain of Arizona and former New York City Mayor Rudolph Giuliani, increasingly take the stage, Rove is the point man to protect Bush’s winning formula with social conservatives in next year’s battle for control of Congress. While so many political mechanics in both parties chase elusive swing voters, Rove directed two winning presidential campaigns — and a successful 2002 midterm election — with a dramatically contrarian approach. Especially on social hot buttons, such as abortion and gay rights, he preferred to jettison appeals to moderates and hold the conservative base with hard-line pitches. The resulting high turnout of evangelical Christians and other social conservatives put Bush in the White House, and kept him there for a second term.

5. The Key to Victory. One way to understand Bush’s continuing need for Rove is to fully appreciate their history as a team. They first met in 1973, when Rove, then working for the Republican National Committee (RNC), was sent to the train station to meet Bush and hand him his car keys. Rove was too green at the time to be part of the inner circle of Bush’s father, who was then RNC chairman, but he maintained growing ties with the son, and 20 years after their train station encounter it was his idea for Bush to run for governor of Texas. Somebody else might have showed up to give Bush his car keys those many decades ago, but Rove’s fierce drive and organizational skill got them to the White House.

Indeed, it is hard to imagine Bush abandoning Rove without indisputable evidence — or an indictment — showing that his trusted aide endangered national security. But if that happened, the “turd blossom” would be gone, severely endangering Bush’s chances for a successful second term.

Contributing Editor Craig Crawford is a news analyst for MSNBC, CNBC and “The Early Show” on CBS. He can be reached at ccrawford@cq.com.