Another Tuesday brings another test of country's anti-establishment sentiment

Organized labor faces an Arkansas showdown with the Democratic establishment on Tuesday.

Unions and their allies have spent more than $6.5 million to take down Sen. Blanche Lincoln (D-Ark.) and turn Arkansas into yet another symptom of a national anti-incumbent mood.

Voters will also select Republican challengers for two other endangered incumbent Democrats, Senate Majority Leader Harry ReidHarry ReidThe missed opportunity of JASTA States urged to bolster election security How the White House got rolled on the Saudi-9/11 bill MORE (Nev.) and Sen. Barbara BoxerBarbara BoxerDems gain upper hand on budget Overnight Finance: Senate rejects funding bill as shutdown looms | Labor Dept. to probe Wells Fargo | Fed to ease stress test rules for small banks Funding bill rejected as shutdown nears MORE (Calif.).

But the spotlight will shine brightest on Lincoln, who earned union scorn for opposing a public option in the healthcare bill and refusing to back card- check legislation championed by the labor movement.

Unions and other liberal groups are as angry with some of their erstwhile allies in the Democratic Party as the Tea Party movement is irked with some Republicans.

Labor groups have emptied their coffers to attack Lincoln and elevate Lt. Gov. Bill Halter, the Democrat who forced Lincoln into a run-off last month.

Momentum appears to be behind Halter, who according to polls is running neck and neck with Lincoln despite, or perhaps because of, support for the incumbent in Washington. Lincoln has been endorsed by President Barack ObamaBarack ObamaDonald Trump will make our economy great again Clinton proposes 'reserve' program for volunteers Trump’s law and order promises won’t make America any safer MORE, and former President Bill ClintonBill ClintonNewsweek hit with cyberattack after posting Trump Cuba story WATCH: Impatient Obama waits for Bill Clinton to board Air Force One Trump’s law and order promises won’t make America any safer MORE, Arkansas’s former governor, is also supporting her.

The Service Employees International Union (SEIU) has spent more than $3 million on the race, according to Federal Election Commission (FEC) records, while the American Federation of State, County and Municipal Employees has spent more than $1.5 million.

Labor groups are also putting activists in the field for what is expected to be a close election. The AFL-CIO has sent staff from its Washington office to help Halter supporters get to the polls, as has Working America, its community affiliate.

Working America’s 41 paid organizers in Arkansas have made 315,000 phone calls and knocked on 120,000 doors, canvassing voters in 27 cities and 17 counties in the state, according to spokeswoman Alison Omens.

The group has also spent more than $1.3 million on ads and has been in Arkansas since the healthcare fight, when it urged constituents to press Lincoln to support the public option.

“Working America organizers are going back to the folks who wrote and their neighbors to let them know that Sen. Lincoln didn’t listen, and that Bill Halter is a choice who will listen to working people’s stories,” Omens said. 

Labor’s opponents have tried to help Lincoln.

The U.S. Chamber of Commerce, which fought unions on the public option and card-check, spent $300,000 on ads for Lincoln, according to FEC reports.

In Nevada, the Tea Party Express is supporting former State Assemblywoman Sharron Angle (R), who leads two other Republicans in recent polls.

The conservative Club for Growth has also made significant expenditures in Nevada. According to the FEC, the anti-tax group has spent some $485,000, much of it going to ads that criticize Sue Lowden for raising taxes during her tenure in the state Legislature.

Lowden was once considered the GOP front-runner but has seen her lead slip away. She now trails Angle and Las Vegas businessman Danny Tarkanian in the contest to face Reid, whom polls consistently have shown is in danger this year.

Lowden has fallen because of the way she has handled the media, according to observers. She became the butt of national ridicule when she suggested that bartering could lower the price of medical care and noted that doctors once accepted chickens in exchange for their services. The Democrats branded the incident “chickens for checkups.”

“Her voter contact hasn’t been bad, it’s the way she’s handled the third party assaults,” said Ryan Erwin, an adviser to John Chachas, another Republican Senate candidate in Nevada. “The campaign really misplayed every possible scenario.”

 Lowden’s only hope of a victory is if she’s banked enough ballots during early voting to overcome what’s expected to be an Angle Election Day victory.

Meanwhile, the National Republican Senatorial Committee (NRSC) has started laying the groundwork for an Angle victory.

“If Sharron Angle is the nominee, I’m confident she can beat Harry Reid in November,” NRSC Chairman John CornynJohn CornynHow the White House got rolled on the Saudi-9/11 bill GOP leaders express reservations a day after 9/11 veto override McConnell opens door to changing 9/11 bill MORE (Texas) said during an appearance on Fox News on Monday.

The race for the GOP Senate nomination in California wasn’t supposed to be a close contest and initially attracted little attention.

Once former Rep. Tom Campbell (R-Calif.) shifted out of the gubernatorial race and into the Senate primary, it made the GOP Senate fight competitive.

Former Hewlett-Packard CEO Carly Fiorina (R) is expected to prevail, but could be in rougher condition for her fall battle with Boxer. Fiorina has more baggage coming out of the divisive primary.

“I think she’s made a lot of mistakes, and Campbell caused her a lot of problems,” said a California-based Democratic strategist. “She’s now said a lot of things that will be held against her.”

The strategist pointed to Fiorina’s position in favor of allowing people on the Homeland Security Department’s “no-fly list” to carry and purchase guns as one she’ll come to regret in the general-election race against Boxer.

Michael O’Brien contributed to this report.