He came to power by (mostly) the support of Al-Sadr, a prominent Shiite cleric who is the head of the militia group; The Mehdi Army (estimated to be +60,000 strong).
With the country coming in a brink of civil war in late 2006 (after the bombing of the shrine of Samara) to early 2007 all seemed hopeless, but nope. When President Bush announced the "surge" in January 2007(?) violence has (currently) reached a 4 year low and political progress has been made that would have never have happened if it weren't for the "surge"(IMO). Politically, the parliament has passed an amnesty law: mainly for Sunni captives, giving pensions to ex government officials from the Saddam era, goal reached for having substantial number of security forces, ect.
Once a "liberal" city during the Saddam era, Basra during the most of the war was met with strong religious Shiite militias because of the incompetence of the Britsh
In March of 2008, Maliki gained support of Sunnis for cracking down on Shiite militia in Basra; mostly the Mehdi Army ...