This is answered at paragraphs 129–59. It is summarized simply at para. 158:

“[t]he simplest and most obvious interpretation of a Constitution, if in itself sensible, is the most likely to be that meant by the people in its adoption.” Lake County v. Rollins, 130 U.S. 662, 671 (1889). The most obvious and sensible reading of Section Three, supported by text and history, leads us to conclude that (1) the Presidency is an “office under the United States,” (2) the President is an “officer . . . of the United States,” and (3) the presidential oath under Article II is an oath to “support” the Constitution.

For details of the historical usage and common understanding of the words at issue, you can read paragraphs 129–59 in full. It is fairly plain reasoning.

None of the three separate dissenting judges dissent on that point.

The dissents instead are based in other reasons to find that this barrier in Section 3 does not require Colorado's Secretary of state to exclude Mr. Trump from the upcoming primary ballots, such as:

• that Section 3 is not "self-executing";
• that neither Section 3 nor the relevant election codes obligate the secretary of state to keep a person who is ineligible due to Section 3 off of a primary ballot;
• issues relating to the fact-finding process relied upon;
• etc.

This is answered at paragraphs 129–59. It is summarized simply at para. 158:

“[t]he simplest and most obvious interpretation of a Constitution, if in itself sensible, is the most likely to be that meant by the people in its adoption.” Lake County v. Rollins, 130 U.S. 662, 671 (1889). The most obvious and sensible reading of Section Three, supported by text and history, leads us to conclude that (1) the Presidency is an “office under the United States,” (2) the President is an “officer . . . of the United States,” and (3) the presidential oath under Article II is an oath to “support” the Constitution.

For details of the historical usage and common understanding of the words at issue, you can read paragraphs 129–59 in full. It is fairly plain reasoning.

None of the three separate dissenting judges dissent on that point.

The dissents instead are based in other reasons to find that this barrier in Section 3 does not require Colorado's Secretary of state to exclude Mr. Trump from the upcoming primary ballots, such as:

• that Section 3 is not "self-executing";
• that neither Section 3 nor the relevant election codes obligate the secretary of state to keep a person who is ineligible due to Section 3 off of a primary ballot;
• issues relating to the fact-finding process relied upon;
• etc.

Ohwilleke's answer summarizes the dissenting reasons in more detail.

This is answered at paragraphs 129–59. It is summarized simply at para. 158:

“[t]he simplest and most obvious interpretation of a Constitution, if in itself sensible, is the most likely to be that meant by the people in its adoption.” Lake County v. Rollins, 130 U.S. 662, 671 (1889). The most obvious and sensible reading of Section Three, supported by text and history, leads us to conclude that (1) the Presidency is an “office under the United States,” (2) the President is an “officer . . . of the United States,” and (3) the presidential oath under Article II is an oath to “support” the Constitution.

For details of the historical usage and common understanding of the words at issue, you can read paragraphs 129–59 in full. It is fairly plain reasoning.

The dissents do not dissent on this point. The dissents are based in other reasons to find that this barrier in Section 3 does not require Colorado's Secretary of state to exclude Mr. Trump from the upcoming primary ballots, such as:

• that it is not "self-executing";
• that it does not impose an obligation on the secretary of state in relation to primary ballots;
• issues relating to the fact-finding process relied upon;
• etc.

This is answered at paragraphs 129–59. It is summarized simply at para. 158:

“[t]he simplest and most obvious interpretation of a Constitution, if in itself sensible, is the most likely to be that meant by the people in its adoption.” Lake County v. Rollins, 130 U.S. 662, 671 (1889). The most obvious and sensible reading of Section Three, supported by text and history, leads us to conclude that (1) the Presidency is an “office under the United States,” (2) the President is an “officer . . . of the United States,” and (3) the presidential oath under Article II is an oath to “support” the Constitution.

For details of the historical usage and common understanding of the words at issue, you can read paragraphs 129–59 in full. It is fairly plain reasoning.

None of the three separate dissenting judges dissent on that point. 

The dissents instead are based in other reasons to find that this barrier in Section 3 does not require Colorado's Secretary of state to exclude Mr. Trump from the upcoming primary ballots, such as:

• that Section 3 is not "self-executing";
• that neither Section 3 nor the relevant election codes obligate the secretary of state to keep a person who is ineligible due to Section 3 off of a primary ballot;
• issues relating to the fact-finding process relied upon;
• etc.