The House will begin the public phase of its impeachment inquiry Wednesday with Democrats and Republicans prepared to offer competing narratives of whether President Trump inappropriately pressured Ukraine to investigate his political rivals, during televised hearings that could determine the fate of his presidency.

Diplomats and career government officials, they’re little known outside professional circles, but they’re about to become household names testifying in the House impeachment inquiry .

Bernie Sanders rallied hundreds of supporters outside the New Hampshire capital when the senator formally filed to compete in the state’s first-in-the-nation presidential primary. A howling crowd cheered South Bend, Indiana, Mayor Pete Buttigieg as he walked through the statehouse to file his paperwork.

Michael R. Bloomberg is actively preparing to enter the Democratic presidential primary and is expected to file paperwork this week designating himself as a candidate in at least one state with an early filing deadline, people briefed on Mr. Bloomberg’s plans said.

The U.S. officials who will testify next week at public hearings in the House of Representatives impeachment probe against President Donald Trump include the current top diplomat in Ukraine, the previous ambassador there and a diplomat who has spent much of his career fighting corruption in Ukraine and elsewhere.