Call it the halftime push for closing up the Republican primaries.  With the next primaries eight days away, prominent Republicans and conservatives endorsed Mitt Romney over the last 24 hours.  Most prominent among them was Senator Mike Lee, who rallied grassroots Tea Party support in Utah two years ago to give then-incumbent Bob Bennett the boot:

Washington • Conservatives will start flocking to presidential candidate Mitt Romney, Sen. Mike Lee predicted Sunday as he offered his endorsement to the man he believes will be the best Republican to take on President Barack Obama.

“This is a pretty critical year,” Lee said in an interview. “There are big decisions for the country to make and … I think we would be well-advised as Republicans to start getting behind our eventual nominee.”

Lee, the last of Utah’s Republicans in Congress to formally endorse Romney, said the time has come for conservatives to rally behind the former Massachusetts governor and start creating the national effort to oust Obama.

Romney figures to be a very popular figure in Utah anyway, and not just because of his Mormon religion.  Romney built a lot of goodwill and support for his role in rescuing the Salt Lake City Olympics from financial disaster, and people in Utah have not forgotten it.  Lee’s endorsement could be considered a move to keep up with constituent opinions, but also could be a game changer among Tea Party activists.  Lee won his Senate seat through their efforts, and his late endorsement might convince the grassroots to start throwing in with the current frontrunner in the race.

Carly Fiorina was less successful in her own Senate bid in 2010, and is considered to be more of a Republican party moderate, so her endorsement probably won’t carry as much impact:

Carly Fiorina, a former chief executive officer of Hewlett-Packard Co. (HPQ), endorsed Mitt Romney for the Republican presidential nomination today, describing the former Massachusetts governor as the candidate best able to beat President Barack Obama in November.

“While I also admire his opponents, it is now clear that Mitt Romney is the candidate most able to defeat Barack Obama in November,” Fiorina said in a statement. “This election is too important to lose and that’s why I urge my fellow Republicans to join me in supporting Mitt Romney.”

Among conservatives, American Conservative Union chair Al Cardenas might have more impact.  He also endorsed Romney today:

As of today, it is clear neither Senator Santorum nor Speaker Gingrich nor Congressman Paul can amass the majority of delegates required to be the Republican nominee. Their only paths to victory feature a contested, anarchic floor fight just weeks before Americans vote on whether or not to give President Obama a second term.

With all due respect to my fellow conservative leaders determined to oppose Governor Romney, that is not a worthy endeavor. For the sake of our Republic, I’m not willing to wait until the Republican National Convention to sort this out. It’s time to unite behind a worthy presidential candidate, build our organization and raise the resources necessary to defeat the liberal electoral machine. …

Governor Romney is an honorable, worthy, competent, conservative candidate for our next commander-in-chief. I’m proud to support his campaign for president. His opponents ran great races and all four men became better candidates because of the effort. I thank and congratulate them all on their contributions to the race, but their time is over.

I’m calling on my fellow conservatives, for goals both lofty and pragmatic, to join me in supporting the only candidate that can ensure President Obama’s legacy is limited to just four years of fiscal irresponsibility and disregard for our Constitution, and not eight.

House Majority Whip Kevin McCarthy concurs:

In his statement, McCarthy said Republicans “need to unite” around a candidate Romney.

“After a long and grueling primary, it is clear that Mitt Romney is the best candidate to face President Obama and fix the mess of his one and only term,” McCarthy said.

Every primary fight hits a tipping point in which voters start climbing onto the bandwagon of the frontrunner.  Clearly, a spectrum of Republican leaders want to push that tipping point up as soon as possible.  The question will be whether voters will listen.  However, thanks to the primary schedule, Santorum is very vulnerable to a tipping-point scenario in April.  Only two states give him a solid chance for victories next month, Wisconsin and Pennsylvania, and a loss in either (or both, especially with Pennsylvania being Santorum’s home state) could force that tipping point, even though May’s schedule is a lot more friendly to Santorum.

Look for even more prominent figures to announce endorsements this week, but I doubt they will have any immediate impact.  The GOP wants to bring this to an end as quickly as possible, but it’s not likely that Santorum will get out without contesting at least a few more of these states.  Only if Santorum can’t win in Wisconsin and Pennsylvania will he be inclined to withdraw.