Leading presidential candidate to clinch nomination Tuesday

As the four remaining Republican presidential candidates battle for delegates in Tuesday night's primaries, the man they hope to unseat in November -- President Barack Obama -- will quietly clinch his party's nomination for a second term as the polls close in Maryland and the District of Columbia at 8:00 p.m.

Like his Republican counterparts, President Obama has been competing in primaries and caucuses this year and picking up delegates along the way. Unlike the Republicans, Obama faces no serious opposition in his quest for renomination.

According to CNN's delegate estimate, the president has 2,735 of the 2,778 delegates needed to secure his party's nod. He is expected to win most or all of the 119 delegates at stake in Maryland and D.C., as well as the 100 delegates at stake in Wisconsin later in the evening.

The milestone comes just shy of the one year anniversary of the president's re-election announcement on April 4, 2011. The last incumbent president running for re-election, Republican George W. Bush, clinched the 2004 GOP nomination on March 9 in a nomination season that was more heavily front-loaded than in 2012.

On the Republican side, Mitt Romney is expected to reach a campaign milestone of his own. If he wins just one delegate in any of Tuesday's contests, he will reach the half-way mark in the GOP race for delegates. The former Massachusetts governor currently has 571 of the 1,144 delegates needed to win the Republican nomination.