As this column is being written on March 23, Republican primary voters in Louisiana are preparing to go to the polls to express their choices for the Republican nominee for president. By the time Louisiana has its turn in presidential primaries, the nominee often has already been determined. Though there is a heavy favorite at this point in the race, Louisiana’s primary will have at least some impact this go around.

The crowded field of GOP candidates has been winnowed to four—with two on political life support—as the Bayou State voters head to the polls. Simply put, Rick Santorum needs to win the Louisiana primary convincingly and follow it up in quick succession with other primary wins to remain a major factor in the race. Even if he accomplishes that scenario, Santorum faces an extremely uphill climb to the nomination.

It takes 1,144 delegates to win the Republican nomination. According to the Associated Press, prior to the Louisiana primary, Mitt Romney has 563 delegates; Santorum has 263; and Newt Gingrich trails badly with 135. Gingrich’s chances basically vanished when he finished significantly behind Santorum recently in Alabama and Mississippi—two states vital to his “southern strategy” approach. If he loses to Santorum in Louisiana—particularly if he finishes behind Romney—he will be in the race in name only if he continues to compete.

Only 20 delegates are up for grabs in Louisiana’s March 24 primary. The other 26 will be allocated at caucuses at a later date. Santorum should garner a majority of the Louisiana delegates. It is absolutely imperative that he captures the 42 delegates in Wisconsin’s “winner take all” primary on April 3 because Romney is expected to take the 56 delegates available in Maryland and the District of Columbia on the same day. Even so, that would mean that Santorum would only slightly cut into Romney’s 300 delegate lead by the time the votes are cast on April 3. After that, the going gets tough for Santorum.

Romney is likely to capture the lion’s share of the 159 delegates to be decided in New York, Rhode Island, Connecticut, and Delaware on April 24. Santorum should do well in his home state of Pennsylvania on that date, but he won’t stop Romney from getting some of the 72 delegates available. The absolute make-or-break portion of the primary calendar for Santorum is the May 8 primaries in North Carolina, Indiana, and West Virginia. He would need to win these three states convincingly to capture critical momentum for the last rung of the primaries. In all likelihood, Romney will have over 800 delegates coming out of those May 8 primaries. He is the odds-on favorite to win California’s 172 delegates and New Jersey’s 50 on June 5. Likewise, he is a mortal lock to win Utah’s 40 on June 26. That would likely place Romney at or above the 1,100 mark, not including any additional delegates he would gain in eight other primaries to be contested between Louisiana and the final primary in Utah.

The GOP primaries have been somewhat unpredictable in 2012. There perhaps still could be a few surprises along the way, but both time and the calendar are running out for the candidates. Santorum either needs to string together numerous big wins starting in Louisiana and continuing in Wisconsin on April 3 or he will see a growing number of big name Republicans endorsing Romney and calling for unity behind him. That trend has already started. Santorum must generate high levels of momentum quickly to convince Republican voters that he has something better than a puncher’s chance to win the nomination and beat Barack Obama on November 6.