Mr. Pappas, a 44-year-old Democratic congressman, is the first major candidate to enter the race to succeed the retiring Senator Jeanne Shaheen.

Four-term Congressman Chris Pappas of New Hampshire has announced his bid to succeed retiring U.S. Sen. Jeanne Shaheen, a fellow Democrat, next year.

Rep. Chris Pappas is entering the race for New Hampshire’s open Senate seat. The fourth-term congressman is the first high-profile candidate to launch a campaign to succeed Sen. Jeanne Shaheen, a fellow Democrat who is retiring after three terms.