A couple of observations about the loss by Rep. Mark Sanford, R-S.C., to GOP challenger Katie Arrington in the primary last night.

Is Arrington’s victory reflective of the President’s political clout heading into the midterm elections?

Perhaps. Midterm elections are often a demonstration of what the country thinks of the president. But Tuesday night wasn’t a midterm election. It was a primary. In fact, it was a primary in a very red state which is very supportive of President Trump. Primaries and special elections are all about voter turnout and who energizes people to get to the polls.

In many respects, Sanford was caught flat-footed by his challenger. Arrington came out swinging with pro-Trump ads. Sanford then had to go on the defensive to counter punch.

Keep in mind that the president didn’t tweet support for Arrington until late in the day yesterday. By that point, people were either engaged in the Sanford-Arrington tilt or they weren’t. The die was cast.

So, the president wields leverage in South Carolina. That tells us a lot about primaries. But not the midterm in the fall.

Perhaps a better test of President Trump’s political acumen falls in a battleground state like Nevada. For instance, Mr. Trump personally persuaded Danny Tarkanian - the son of legendary UNLV basketball coach Jerry Tarkanian - to forgo his primary challenge against Sen. Dean Heller, R-Nev., and run for the House instead. The Tarkanian surname is of legend in the Silver State thanks to success on the court with the elder Tarkanian. But the son has failed to capitalize on his father’s fame, failing in multiple House and Senate bids over the years.

That says a lot in Nevada.

Las Vegas casinos and hotels dimmed their lights on the Strip when Jerry Tarkanian died in 2015. It’s an honor usually reserved to note the passing of presidents and Vegas icons like Dean Martin and Elvis Presley. Yet the younger Tarkanian struggles to translate that into political success.

That said, Tarkanian nearly defeated Rep. Jacky Rosen, D-Nev., for her seat in 2016. Neither candidate hit the 50 percent threshold. Mr. Trump carried the Congressional district by a single point. However, Hillary Clinton won Nevada’s six electoral vote, edging the president by about two-and-a-half points. That’s why Nevada is a true swing state. A good yardstick to measure the president’s political juice could come in Nevada.

Interestingly, Tarkanian did not mention the president in a statement touting his primary win. However, Tarkanian did rip a page out of Mr. Trump’s playbook. Tarkanian faces Democrat Susie Lee in November to succeed Rosen... who is running for the Senate. Tarkanian promptly bequeathed Lee with a nickname, ala the president: “Socialist Susie.”

Unclear if those tactics will work in a swing state like Nevada.

This comes amid Rep. Chris Collins, R-N.Y., telling colleague Anne Ball that “President Trump is one of if not the most popular presidents with Republicans in history.” Collins said, “If you’re not on the same page as the president and 85 to 90 percent of your base is, you can see where that can cause a problem.”

Another barometer worth watching hovers around Senate Foreign Relations Committee Chairman Bob Corker. The Tennessee Republican excoriated fellow GOP senators on the floor over trade. Corker is livid because Republican senators complain about the president’s imposition of tariffs on national security grounds. However, the GOP leadership blocked Corker from offering an amendment entailing Congressional oversight when a president invokes “national security” for tariffs as Mr. Trump did with Canada.

“Ready, fire, aim! Ready, fire, aim!” thundered Corker about what he considers a slapdash trade policy by the Trump administration.

Corker upbraided fellow senators for their subservience to the president, even though most publicly fretted that tariffs will wound the nation economically.

“We might poke the bear,” chastised Corker. “We can’t do that because we’d be upsetting the president of the United States! The president of the United States! I can’t believe it!”

Whether lawmakers begin to vigorously join Corker and challenge the president on trade or remain reticent could be another way to measure Mr. Trump’s political brawn this fall.

Fox News' Anne Ball contributed to this report.