President Trump's approval ratings have declined in all but one state with a competitive 2018 Senate race, but he's only below 50% in four of the 10 Trump-voting states with vulnerable Democratic senators, according to Morning Consult's monthly tracking poll.

Why it matters: To win the Senate — a goal that's less likely than winning the House — Democrats would need to win 14 of these 17 races. And with a packed fall campaign schedule, Trump plans to make the midterms more, not less, of a referendum on him.

Among the races classified by Cook Political Report as "likely" Democrat or Republican, "lean" Democrat or Republican, or "tossup":

• Trump has lost the most ground since inauguration in Arizona, Florida, North Dakota, Wisconsin, and Michigan.
• Of the 10 Trump-voting states with vulnerable Democratic senators, he is below 50% approval in four of them (Ohio, Pennsylvania, Michigan, and Wisconsin) and at 50% in two others (North Dakota and Florida).
• He's above 50% in the rest, and soaring at 63% approval in West Virginia.

The bottom line: Trump's approval ratings are well below 50% nationally — and that's the level where the president's party usually loses more congressional seats in midterm elections. But the state-by-state map shows us why the Senate isn't as vulnerable as the House.