Democrats strengthened control of the Senate on Tuesday by capitalizing on public discontent with Republicans and the sagging economy, but they seem unlikely to win a filibuster-proof majority.

The night was already historic with the election of Barack Obama as the nation's first black president. And what is unfolding as a big night for Senate Democrats, the party picked up Republican seats in North Carolina, New Mexico, Virginia, Colorado and New Hampshire. Including two Independents who caucus with them, Democrats now hold a 56-to-44 majority, with several races still to be decided.

Polling has found Democratic challengers ahead in other states — Alaska, Minnesota and Oregon.

The only vulnerable Democrat in cycle, Sen. Mary Landrieu of Louisiana, appears to have held off her challenger John Kennedy, leading 50 to 47 percent with 91 percent of the precincts reporting. 

To reach 60 votes, Democrats needed to win a race in the Deep South, but Republican Roger Wicker appears to have held off former Gov. Ronnie Musgrove (D). And Republican Saxby Chambliss leads Democratic challenger Jim Martin 56 percent to 40 with 73 percent of precincts reporting.

Senate Minority Leader Mitch McConnell, a top target by national Democrats, held off a strong Democratic challenge by businessman Bruce Lunsford, a rare bright spot for the GOP.

If Chambliss holds Martin off, the maximum number of seats Democrats could win is 59, a stark change from the 109th Congress, when they held only 45 seats.

Other victors include Democrat Kay Hagan, 45, a five-term state senator, who now becomes North Carolina's second female senator in the traditionally Republican state. With 84 percent of precincts reporting, Hagan was up 53 percent to 44 against Dole.

Hagan rode a Democratic wave that pummeled the 72-year-old Dole — the wife of former Sen. Bob Dole (R) — and other GOP incumbents because of voter discontent with President Bush and the sagging economy. She and the senator engaged in an acrimonious final week of the campaign, with Dole accusing Hagan of taking money from a "godless" group and Hagan defending her Christian roots.

Also riding that wave was former New Hampshire Gov. Jeanne Shaheen, who defeated first-term Sen. John Sununu (R) in that state. Shaheen, a veteran political force in the Granite State, lost the Senate race to Sununu in 2002 by a 47-51 percent.

The victories follow a win by Democrat Mark Warner, the former governor of Virginia, who easily won the state’s open Senate seat. Warner defeated Republican Jim Gilmore, also a former governor, in the fight for the seat held by retiring Sen. John Warner (R), a five-term senator and one of the chamber’s most respected voices on foreign policy. Warner's victory represents a Democratic transformation of a state that was dominated by Republicans just four years ago.

Mark Warner, who is not related to John Warner, is a rising star in the Democratic Party. Having toyed with mounting a presidential bid in 2008, the former Virginia governor later decided instead to run for the Senate. This is not his first foray into Washington politics, however. After obtaining his law degree from Harvard University, Warner worked on the staff of Sen. Chris Dodd (D-Conn.) in the early 1980s.

After leaving Capitol Hill and making a fortune in a telecommunications firm, he unsuccessfully ran for the Senate in 1996 against John Warner. In 2001, he became governor of the once GOP-dominant state and left office with high favorability ratings. His stature has since skyrocketed in Democratic circles, and he delivered the keynote address at the party’s 2008 nominating convention.

Aaron Blake contributed to this article.

.