Kathy Barnette, a Republican Senate candidate in Pennsylvania who has climbed in the polls against two big-spending rivals, on Sunday sought to downplay her past Islamophobic messages on social media, telling a Fox News host that some of them were “not even full thoughts,” nor “even full sentences” but rather, prompts intended to facilitate a conversation.

The “Fox News Sunday” host, Shannon Bream, asked Ms. Barnette about specific messages she had written on Twitter. In 2014, Ms. Barnette wrote, “If you love freedom, Islam must NOT be allowed to thrive under any condition.” In 2016, Ms. Barnette wrote, “Obama is aMuslim. Doing Muslim like THINGS!”

At first, Ms. Barnette blamed former President Barack Obama and the people who had fled the civil war in Syria, telling Ms. Bream, “In almost all of those tweets, when you look at the time frame we were living in at that particular time, we had the Obama administration bringing in a lot of Syrian refugees at that time.”

Ms. Barnette was spreading the toxic brew of misinformation that Donald J. Trump helped popularize among Republicans before his successful presidential run in 2016, including the false claim that Mr. Obama is Muslim. He is a Christian. And despite Mr. Obama’s pledge to welcome 10,000 Syrian refugees, only a fraction of them had entered the United States when Ms. Barnette posted her message.

Ms. Barnette has spread falsehoods on social media and in public speeches aimed at Muslims for years. In an NBC interview on Friday she falsely denied writing a statement that is still on her Twitter timeline from 2015: “Pedophilia is a Cornerstone of Islam.”

Ms. Barnette describes herself as an author, social conservative and Christian. She has recently surged in public polling against her two rivals in the Republican Senate primary, Dr. Mehmet Oz and David McCormick. She was endorsed by the anti-tax group Club for Growth, which committed $2 million for advertising to support her. The primary is on Tuesday.

Her sudden rise, and the accompanying scrutiny, have worried Republican leaders, who believe she may cost the party a chance to win an open Senate seat in the November election.

Former President Donald J. Trump, who has endorsed Dr. Oz, said in a public statement last week, “Kathy Barnette will never be able to win the general election against the radical left Democrats.”

On Sunday, Ms. Barnette sought to distance herself from her previous messages, saying they were incomplete thoughts and that she cannot explain them because she wrote them years ago.

“At that time, I was hosting a show called ‘Truth Exchange’ and I would have all kinds of ideas and was leaning in to helping the public begin to have those conversations, and so those were some of the — that’s the context around a lot of those tweets,” Ms. Barnette said on Sunday. “The overwhelming majority of the tweets that are now being presented are not even full thoughts. They’re not even full sentences and yet people take it and they begin to build their own narrative around it.

Ms. Barnette continued: “So, I can’t provide a lot of context because, again, it’s almost 10 years ago. That’s how far they have to go back to find anything on me.”