Republican U.S. presidential candidate Donald Trump continued his war of words with GOP rival Jeb Bush Friday night, with the real-estate mogul again tweeting at the former Florida governor about his brother’s time as president. Trump called Jeb Bush “pathetic” and doubled down on earlier comments indicating former President George W. Bush should be held at least partially responsible for the terrorist attacks of Sept. 11, 2001:

No @JebBush, you’re pathetic for saying nothing happened during your brother’s term when the World Trade Center was attacked and came down. — Donald J. Trump (@realDonaldTrump) October 17, 2015





Trump followed up with another tweet suggesting Jeb Bush was unfit to be president:

.@JebBush, like it or not, our country needs more energy and spirit than you can provide! #MakeAmericaGreatAgain — Donald J. Trump (@realDonaldTrump) October 17, 2015

The latest back-and-forth exchange between the two candidates began Friday morning when Trump questioned Jeb Bush’s assertion that his brother kept the U.S. safe during an interview with Bloomberg TV. “When you talk about George Bush, I mean, say what you want, the World Trade Center came down during his time,” Trump said.

Bush responded by calling Trump’s comments “pathetic” later in the day.

The tiff between the two candidates actually started to gather steam during the second Republican presidential debate when Trump addressed Jeb Bush directly and asserted that George W. Bush was responsible for the election of President Barack Obama.

“Your brother and your brother’s administration gave us Barack Obama because it was such a disaster those last three months that Abraham Lincoln couldn’t have been elected,” Trump said at the time.

Bush responded with what has become a rallying call for his campaign, insisting that his brother kept Americans safe. “As it relates to my brother, there’s one thing I know for sure: He kept us safe,” Bush replied. “I don’t know if you remember, Donald -- you remember the rubble? You remember the firefighter with his arms around him? He sent a clear signal that the United States would be strong and fight Islamic terrorism, and he did keep us safe.”

How pathetic for @realdonaldtrump to criticize the president for 9/11. We were attacked & my brother kept us safe. — Jeb Bush (@JebBush) October 16, 2015

Jeb Bush has yet to respond to Trump’s latest insults on Twitter.