Assailing each other with no letup, Republican front-runner Donald Trump and challenger Ted Cruz traded insults, charges and more Tuesday as Indiana voters went to the polls in what could be an all-but-decisive presidential primary election.
In the Democratic race, Vermont Sen. Bernie Sanders was angling for a victory over Hillary Clinton, though a win was unlikely to slow her march to the party's nomination. Clinton has 91 percent of the delegates she needs to become the first woman nominated by a major party.
Texas Sen. Cruz, who is facing a critical moment for his struggling campaign, unleashed a blistering attack against Trump, calling the businessman "amoral" and warning the country could "plunge into the abyss" if he is elected president.
Trump, growing increasingly confident about his chances of clinching the GOP nomination, responded by saying Cruz "does not have the temperament to be president of the United States." Earlier Tuesday Trump had rehashed unsubstantiated claims that the Texan's father, Rafael Cruz, appeared in a 1963 photograph with John F. Kennedy's assassin, Lee Harvey Oswald - citing a report first published by the National Enquirer.
"His father was with Lee Harvey Oswald prior to Oswald's being, you know, shot," Trump said on Fox & Friends. "Nobody even brings it up; I mean they don't even talk about that."
The heated exchanges come as Cruz's opportunities to block Trump dwindle. While Indiana's primary once looked like a ripe opportunity for the conservative Texas senator to make up ground, his campaign has faltered here and aides were pessimistic about their prospects.
During one of his final stops in the state, a visibly exasperated Cruz let his frustrations with Trump fly, calling him a "pathological liar," a "serial philanderer," "kooky," "nuts" and "terrified with strong women."
Like Cruz, Sanders faces a difficult path to overtaking his party's front-runner. Sanders conceded his strategy hinges on persuading superdelegates to back him over the former secretary of state. Superdelegates are Democratic Party insiders who can support the candidate of their choice, regardless of how their states vote. And they favor Clinton by a nearly 18-1 margin.
Neither Clinton nor Sanders were in Indiana Tuesday. Sanders was making stops in Kentucky, which holds a primary in mid-May, while Clinton moved on to Ohio, a key general election battleground.
Polling of voters after they cast their ballots looked more promising for the Democrats than the Republicans come November. Only about half of Indiana's Republican primary voters said they were excited or even optimistic about any of their remaining candidates becoming president. Still, most said they probably would support whoever won for the GOP.
About 7 in 10 Democrats said they'd be excited or at least optimistic about either a Clinton or Sanders presidency. Most said they would support either in November.
A fall showdown between Clinton and Trump would pit one of Democrats' most experienced political figures against a first-time candidate who is deeply divisive within his own party. Cruz and other Republicans have argued that Trump would be roundly defeated in the general election, denying their party the White House for a third straight term.
Still, Trump has won six straight primary contests and has 80 percent of the delegates needed to secure the GOP nomination. Cruz, as well as Ohio Gov. John Kasich, can only hope to keep him from the 1,237 delegates he needs and push the GOP race to a contested convention.
Cruz has spent the past week camped out in Indiana, securing the support of the state's governor and announcing Carly Fiorina, the retired technology executive, as his running mate. But his aides were cautious heading into voting, and campaign officials had been told to prepare for Cruz to deliver "a very somber" speech Tuesday night in Indianapolis, according to one aide who spoke on the condition of anonymity to share internal discussions.
Trump, too, devoted more time to campaigning in Indiana than he has to most other states, underscoring his eagerness to put his Republican rival away and shift his attention toward Clinton.
While Trump cannot clinch the nomination with a win in Indiana, his path would become easier and he would have more room for error in the campaign's final contests. After Cruz's comments in Evansville, he said in a statement the Texas senator was "a desperate candidate trying to save his failing campaign."
Cruz said America is "looking, potentially, at the Biff Tannen presidency," referencing a character in the "Back to the Future" films. He described the character as "a braggadocious, arrogant buffoon who builds giant casinos with giant pictures of him everywhere he looks."
The film's screenwriter Bob Gale told the Daily Beast last year that the character was based on Trump.
Republican leaders spent months dismissing Trump as little more than an entertainer who would fade once voting started. Cruz was among those who actively tried to align themselves with Trump and called him "terrific."
As Trump began to pick up wins, Cruz became more critical of his rival's policies. Still, his torrent of attacks Tuesday was by far the most pointed and personal of the campaign to date.