A top GOP senator said testimony from former national security adviser John Bolton could be a boon to President Trump in a Senate impeachment trial.

Texas Sen. John Cornyn, the No. 2 Republican in the upper chamber, voiced a willingness to vote in favor of subpoenaing Bolton to testify but only after he learns what the ex-Trump adviser has to say.

"I would want to know what he has to offer that would help eliminate the issues, the two articles of impeachment, that have been issued by the House of Representatives. That would define the scope of any Senate trial," he said in an interview Monday on Fox News Radio's The Guy Benson Show.

Bolton, 71, issued a statement hours earlier saying he would not fight a subpoena to testify, marking a shift from his refusal to testify before House investigators on orders from the White House. The House passed two articles of impeachment nearly three weeks ago that charged Trump with abuse of power in dealing with Ukraine and obstruction of Congress.

Bolton's announcement gave ammunition to Democrats in the House and Senate who are pressuring Senate Majority Leader Mitch McConnell to allow witnesses, but Cornyn said the former White House official's offer could hurt their impeachment case.

"I think it’s entirely likely that his testimony would be helpful to the president because it would identify basically a foreign policy dispute, which is reserved to the president under the Constitution, really his sole authority, as a basis for impeachment, for this now the third time in American history. So, it could well be beneficial to the second count, which is obstruction," Cornyn said.

House Speaker Nancy Pelosi, a Democrat from California, has been withholding articles of impeachment because McConnell has signaled he may not call any witnesses. The Kentucky Republican said he will not agree in advance to the Democrats' demands.

“The House may have been content to scrap their own norms to hurt President Trump, but that is not the Senate,” McConnell said Monday. “Even with a process this constitutionally serious, even with tensions rising in the Middle East, House Democrats are treating impeachment like a political toy.”